Tag Archives: Cosmology and Extragalactic Astrophysics

U'(1) Neutrino Interaction at Very Low Energies [CL]

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http://arxiv.org/abs/1402.4537


A procedure for studying low energy neutrinos processes using hadronic physics ideas is proposed. We describe how the neutrino-neutrino interactions can be modelled using massive gauge theories. The mass of the gauge bosons is created by spontaneous symmetry breaking and we show that relationship between mass, currents and potential gauge is through vector dominance, i.e. $J_\mu = M^2 A_\mu$. A tiny charge $U(1)$ for neutrinos is turned on for energies around the temperature of the cosmic neutrinos background which allow the interaction between neutrinos, above this temperature this interaction disappears. The magnetic flux is quantized in terms of the hidden charge. We found an approximate relation between the order parameter and neutrino condensate $\langle{\bar \nu} \nu\rangle_{\tiny{0}}$. The relation between the neutrino magnetic moment and hidden photons bounds are also discussed.

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J. Gamboa
Fri, 21 Feb 14
41/55

Impact of chromatic effects on galaxy shape measurements [CEA]

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http://arxiv.org/abs/1402.5101


Current and future imaging surveys will measure cosmic shear with a statistical precision that demands a deeper understanding of potential systematic biases in galaxy shape measurements than has been achieved to date. We investigate the effects of using the point spread function (PSF) measured with stars to determine the shape of a galaxy that has a different spectral energy distribution (SED) than the star. We demonstrate that a wavelength dependent PSF size, for example as may originate from atmospheric seeing or the diffraction limit of the primary aperture, can introduce significant shape measurement biases. This analysis shows that even small wavelength dependencies in the PSF may introduce biases, and hence that achieving the ultimate precision for weak lensing from current and future imaging surveys will require a detailed understanding of the wavelength dependence of the PSF from all sources, including the CCD sensors.

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J. Meyers and P. Burchat
Fri, 21 Feb 14
47/55

The Green Valley is a Red Herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies [GA]

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http://arxiv.org/abs/1402.4814


We use SDSS+\textit{GALEX}+Galaxy Zoo data to study the quenching of star formation in low-redshift galaxies. We show that the green valley between the blue cloud of star-forming galaxies and the red sequence of quiescent galaxies in the colour-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies. Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disk to spheroid and star formation is quenched rapidly. In contrast, the majority of blue star-forming galaxies have significant disks, and they retain their late-type morphologies as their star formation rates decline very slowly. We summarize a range of observations that lead to these conclusions, including UV-optical colours and halo masses, which both show a striking dependence on morphological type. We interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs. We conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes. In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, with rapid quenching accompanied by a morphological transformation from disk to spheroid. This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disk to elliptical morphology, and mergers could play a role in inducing black hole accretion and possibly AGN feedback.

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K. Schawinski, C. Urry, B. Simmons, et. al.
Fri, 21 Feb 14
52/55

Giant Sparks at Cosmological Distances? [HEAP]

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http://arxiv.org/abs/1402.4766


[Abridged] Millisecond duration bright radio pulses in the 1.4-GHz band and with inferred dispersion measures (DM) well in excess of Galactic values have been reported by Lorimer et al. and Thornton et al.. The all-sky rate of these events is large, ~10^4 per day above ~1 Jy. To add to the mystery there now exists “Perytons” — also pulsed and dispersed sources but most certainly of local (artificial or atmospheric) origin. The suggested models now range from sources originating in the Earth’s atmosphere, in stellar coronae, in other galaxies and at even cosmological distances. Using a series of physically motivated assumptions combined with the observed properties of these bursts, we explore possible constraints on sites or processes that can account for such high DMs. In our analysis, we focus on the first such reported event by Lorimer et al.: a 30 Jy, 5-ms duration burst with a dispersion measure of 375 cm^-3 pc and exhibiting a steep frequency-dependent pulse width (hereafter dubbed as the Sparker). Assuming that the DM of the Sparker is produced by propagation through a cold plasma and using all available observations we constrain its distance to be greater than 300 kpc. A similar analysis on the four other reported events (all with larger DMs) would lead to a stronger conclusion, namely these “Fast Radio Bursts (FRBs)” (the moniker given to this group by the discoverers) are of extragalactic origin, provided that the inferred DM arises due to propagation through cold plasma. We then explore proposed extra-galactic as well as stellar coronal models for FRBs and find most of them either unable to account for the high daily rate or have difficulty in having an ultra-clean explosion site (essential to the production of high brightness temperature pulse) or suffer from free-free absorption on length scales beyond the immediate production of the radio pulses.

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S. Kulkarni, E. Ofek, J. Neill, et. al.
Thu, 20 Feb 14
6/52

PACS photometry of the Herschel Reference Survey – Far-infrared/sub-millimeter colours as tracers of dust properties in nearby galaxies [GA]

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http://arxiv.org/abs/1402.4524


We present Herschel/PACS 100 and 160 micron integrated photometry for the 323 galaxies in the Herschel Reference Survey (HRS), a K-band-, volume-limited sample of galaxies in the local Universe. Once combined with the Herschel/SPIRE observations already available, these data make the HRS the largest representative sample of nearby galaxies with homogeneous coverage across the 100-500 micron wavelength range. In this paper, we take advantage of this unique dataset to investigate the properties and shape of the far-infrared/sub-millimeter spectral energy distribution in nearby galaxies. We show that, in the stellar mass range covered by the HRS (8<log(M*/Msun)<12), the far-infrared/sub-millimeter colours are inconsistent with a single modified black-body having the same dust emissivity index beta for all galaxies. In particular, either beta decreases, or multiple temperature components are needed, when moving from metal-rich/gas-poor to metal-poor/gas-rich galaxies. We thus investigate how the dust temperature and mass obtained from a single modified black-body depend on the assumptions made on beta. We show that, while the correlations between dust temperature, galaxy structure and star formation rate are strongly model dependent, the dust mass scaling relations are much more reliable, and variations of beta only change the strength of the observed trends.

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L. Cortese, J. Fritz, S. Bianchi, et. al.
Thu, 20 Feb 14
7/52

First Results from the Complete Local-Volume Groups Sample [CEA]

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http://arxiv.org/abs/1402.4676


Galaxy groups form the environment of the majority of galaxies in the local Universe, and many host an extended hot intra-group medium whose radiative cooling appears to fuel, and be stabilised by, feedback from AGN in group-central galaxies. Unfortunately studies of the physical properties of groups and the influence of AGN on their member galaxies and gaseous haloes have been limited by a lack of reliable representative samples of groups in the local Universe. To address this problem, we have assembled the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups within 80 Mpc, which we aim to observe in both low-frequency radio and X-ray wavebands. We here describe results from the first half of the sample, for which X-ray and radio observations are complete. Roughly 55% of the groups have group-scale X-ray halos, of which ~65% have cool cores a similar fraction to that found in galaxy clusters. While 25 of the 26 group central galaxies host radio AGN, among the X-ray bright groups only the cool core systems are found to support central jet sources.

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E. OSullivan, K. Kolokythas, S. Raychaudhury, et. al.
Thu, 20 Feb 14
8/52

Cosmological perturbations and observational constraints on non-local massive gravity [CEA]

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http://arxiv.org/abs/1402.4613


Non-local massive gravity can provide an interesting explanation for the late-time cosmic acceleration, with a dark energy equation of state $w_{\rm DE}$ smaller than $-1$ in the past. We derive the equations of linear cosmological perturbations to confront such models with the observations of large-scale structures. The effective gravitational coupling to non-relativistic matter associated with galaxy clusterings is close to the Newton’s gravitational constant $G$ for a mass scale $m$ slightly smaller than the today’s Hubble parameter $H_0$. Taking into account the background expansion history as well as the evolution of matter perturbations $\delta_m$, we test for these models with the Type Ia Supernovae (SnIa) from the Union 2.1, the Cosmic Microwave Background (CMB) measurements from Planck, a collection of baryon acoustic oscillations (BAO), and the growth rate data of $\delta_m$. Using a higher value of $H_0$ derived from its direct measurement ($H_0 \gtrsim 70$ km s$^{-1}$ Mpc$^{-1}$) the data strongly support the non-local massive gravity model ($-1.1 \lesssim w_{\rm DE} \lesssim -1.04$ in the past) over the $\Lambda$CDM model ($w_{\rm DE}=-1$), whereas for a lower prior (67 km s$^{-1}$ Mpc$^{-1}$ $\lesssim$ $H_0 \lesssim 70$ km s$^{-1}$ Mpc$^{-1}$) the two models are statistically comparable.

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S. Nesseris and S. Tsujikawa
Thu, 20 Feb 14
10/52

Far from equilibrium dynamics of Bose-Einstein condensation for Axion Dark Matter [CL]

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http://arxiv.org/abs/1402.4776


Axions and similar very weakly interacting particles are increasingly compelling candidates for the cold dark matter of the universe. Having very low mass and being produced non-thermally in the early Universe, axions feature extremely high occupation numbers. It has been suggested that this leads to the formation of a Bose-Einstein condensate with potentially significant impact on observation and direct detection experiments. In this note we aim to clarify that if Bose-Einstein condensation occurs for light and very weakly interacting dark matter particles, it does not happen in thermal equilibrium but is described by a far-from-equilibrium state. In particular we point out that the dynamics is characterized by two very different timescales, such that condensation occurs on a much shorter timescale than thermalization.

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J. Berges and J. Jaeckel
Thu, 20 Feb 14
14/52

The impact of a 126 GeV Higgs on the neutralino mass [CL]

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http://arxiv.org/abs/1402.4650


We highlight the differences of the dark matter sector between the constrained minimal supersymmetric SM (CMSSM) and the next-to minimal supersymmetric SM (NMSSM) including the 126 GeV Higgs boson using GUT scale parameters. In the dark matter sector the two models are quite orthogonal: in the CMSSM the LSP is largely a bino and requires large tan$\beta$ from the relic density constraint in most of the parameter space. In the NMSSM the LSP has a large singlino component. We discuss the consequences for the direct dark matter searches, such as the mass spectra and the corresponding WIMP-nucleon cross section. Furthermore, prospects for discovery of XENON1T and LHC at 14 TeV are given.

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C. Beskidt, W. Boer and D. Kazakov
Thu, 20 Feb 14
15/52

Interstellar Silicate Dust in the z=0.685 Absorber Toward TXS 0218+357 [GA]

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http://arxiv.org/abs/1402.4509


We report the detection of interstellar silicate dust in the z_abs=0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data we detect the 10 micron silicate absorption feature with a detection significance of 10.7-sigma. We fit laboratory-derived silicate dust profile templates obtained from literature to the observed 10 micron absorption feature, and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of tau_10=0.49+/-0.02, which rises to tau_10~0.67+/-0.04 if the covering factor is taken into account. We also detected the 18 micron silicate absorption feature in our data with a >3-sigma significance. Due to the proximity of the 18 micron absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 micron, we do not independently fit this feature. We find, however, that the shape and depth of the 18 micron silicate absorption are well-matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 micron feature. The measured 10 micron peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. The reddening, 21-cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems, however. This high optical depth may be evidence for variations in dust grain properties in the ISM between this and the previously studied high redshift galaxies.

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M. Aller, V. Kulkarni, D. York, et. al.
Thu, 20 Feb 14
18/52

General Relativistic Instability Supernova of a Supermassive Population III Star [HEAP]

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http://arxiv.org/abs/1402.4777


The formation of supermassive Population III stars with masses $\gtrsim$ 10,000 Msun in primeval galaxies in strong UV backgrounds at $z \sim$ 15 may be the most viable pathway to the formation of supermassive black holes by $z \sim$ 7. Most of these stars are expected to live for short times and then directly collapse to black holes, with little or no mass loss over their lives. But we have now discovered that non-rotating primordial stars with masses close to 55,000 Msun can instead die as highly energetic thermonuclear supernovae powered by explosive helium burning, releasing up to 10$ ^{55}$ erg, or about 10,000 times the energy of a Type Ia supernova. The explosion is triggered by the general relativistic contribution of thermal photons to gravity in the core of the star, which causes the core to contract and explosively burn. The energy release completely unbinds the star, leaving no compact remnant, and about half of the mass of the star is ejected into the early cosmos in the form of heavy elements. The explosion would be visible in the near infrared at $z \lesssim$ 20 to {\it Euclid} and the Wide-Field Infrared Survey Telescope (WFIRST), perhaps signaling the birth of supermassive black hole seeds and the first quasars.

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K. Chen, A. Heger, S. Woosley, et. al.
Thu, 20 Feb 14
19/52

Astrophysical black holes in screened modified gravity [CEA]

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http://arxiv.org/abs/1402.4737


Chameleon, environmentally dependent dilaton, and symmetron gravity are three models of modified gravity in which the effects of the additional scalar degree of freedom are screened in dense environments. They have been extensively studied in laboratory, cosmological, and astrophysical contexts. In this paper, we present a preliminary investigation into whether additional constraints can be provided by studying these scalar fields around black holes. By looking at the properties of a static, spherically symmetric black hole, we find that the presence of a non-uniform matter distribution induces a non-constant scalar profile in chameleon and dilaton, but not necessarily symmetron gravity. An order of magnitude estimate shows that the effects of these profiles on in-falling test particles will be sub-leading compared to gravitational waves and hence observationally challenging to detect.

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A. Davis, R. Gregory, R. Jha, et. al.
Thu, 20 Feb 14
26/52

A comment on "Exclusion of the remaining mass window for primordial black holes …", arXiv:1401.3025 [CEA]

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http://arxiv.org/abs/1402.4671


In arXiv:1401.3025 a new mechanism of energy loss by primordial black holes passing through neutron stars has been proposed, which is more efficient, by many orders of magnitude, than the existing ones. In this comment we point out a problem in the calculations of arXiv:1401.3025 that may invalidate the result.

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F. Capela, M. Pshirkov and P. Tinyakov
Thu, 20 Feb 14
27/52

The Heating of Mid-Infrared Dust in the Nearby Galaxy M33: A Testbed for Tracing Galaxy Evolution [GA]

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http://arxiv.org/abs/1402.4668


Because the 8 {\mu}m polycyclic aromatic hydrocarbon (PAH) emission has been found to correlate with other well-known star formation tracers, it has widely been used as a star formation rate (SFR) tracer. There are, however, studies that challenge the accuracy and reliability of the 8 {\mu}m emission as a SFR tracer. Our study, part of the Herschel M33 Extended Survey (HERM33ES) open time key program, aims at addressing this issue by analyzing the infrared emission from the nearby spiral galaxy M33 at the high spatial scale of 75 pc. Combining data from the Herschel Space Observatory and the Spitzer Space Telescope we find that the 8 {\mu}m emission is better correlated with the 250 {\mu}m emission, which traces cold interstellar gas, than with the 24 {\mu}m emission. The L(8)/L(24) ratio is highly depressed in 24 {\mu}m luminous regions, which correlate with known HII regions. We also compare our results with the dust emission models by Draine & Li (2007). We confirm that the depression of 8 {\mu}m PAH emission near star-forming regions is higher than what is predicted by models; this is possibly an effect of increased stellar radiation from young stars destroying the dust grains responsible for the 8 {\mu}m emission as already suggested by other authors. We find that the majority of the 8 {\mu}m emission is fully consistent with heating by the diffuse interstellar medium, similar to what recently determined for the dust emission in M31 by Draine at al. (2013). We also find that the fraction of 8 {\mu}m emission associated with the diffuse interstellar radiation field ranges between 60% and 80% and is 40% larger than the diffuse fraction at 24 {\mu}m.

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M. Calapa, D. Calzetti, B. Draine, et. al.
Thu, 20 Feb 14
29/52

An Interacting model of Dark Energy in Brans-Dicke theory [CL]

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http://arxiv.org/abs/1402.4291


In this paper it is shown that in non-minimally coupled Brans-Dicke theory containing a self-interacting potential, a suitable conformal transformation can automatically give rise to an interaction between the normal matter and the Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as the quintessence matter, it has been shown that such a non-minimal coupling between the matter and the scalar field can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans-Dicke parameter $\omega$. We have also studied the observational constraints on the model parameters considering the Hubble and Supernova data.

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S. Das and A. Mamon
Thu, 20 Feb 14
34/52

An exposition on Friedmann Cosmology with Negative Energy Densities [CEA]

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http://arxiv.org/abs/1402.4522


How would negative energy density affect a classic Friedmann cosmology? Although never measured and possibly unphysical, certain realizations of quantum field theories leaves the door open for such a possibility. In this paper we analyze the evolution of a universe comprising varying amounts of negative energy forms. Negative energy components have negative normalized energy densities, $\Omega < 0$. They include negative phantom energy with an equation of state parameter $w<-1$, negative cosmological constant: $w=-1$, negative domain walls: $w=-2/3$, negative cosmic strings: $w=-1/3$, negative mass: $w=0$, negative radiation: $w=1/3$ and negative ultralight: $w > 1/3$. Assuming that such energy forms generate pressure like perfect fluids, the attractive or repulsive nature of negative energy components are reviewed. The Friedmann equation is satisfied only when negative energy forms are coupled to a greater magnitude of positive energy forms or positive curvature. We show that the solutions exhibit cyclic evolution with bounces and turnovers.The future and fate of such universes in terms of curvature, temperature, acceleration, and energy density are reviewed. The end states are dubbed Big Crunch, Big Void, or Big Rip and further qualified as “Warped”, “Curved”, or “Flat”, “Hot” versus “Cold”, “Accelerating” versus “Decelerating” versus “Coasting”. A universe that ends by contracting to zero energy density is termed “Big Poof.” Which contracting universes “bounce” in expansion and which expanding universes “turnover” into contraction are also reviewed.

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R. Nemiroff, R. Joshi and B. Patla
Thu, 20 Feb 14
41/52

AGN-driven outflows without quenching in simulations of high-redshift disk galaxies [CEA]

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http://arxiv.org/abs/1402.4482


Recent observations have revealed nuclear outflows in high-redshift, star forming galaxies. We study outflows driven by Active Galactic Nuclei (AGNs) using high- resolution simulations of idealized z=2 isolated disk galaxies. Episodic accretion events lead to outflows with velocities >1000 km/s and mass outflow rates up to the star formation rate (several tens of Msun/yr). Outflowing winds escape perpendicular to the disk with wide opening angles, and are typically asymmetric (i.e. unipolar) because dense gas above or below the AGN in the resolved disk inhibits outflow. Owing to rapid variability in the accretion rates, outflowing gas may be detectable even when the AGN is effectively “off.” The highest velocity outflows are concentrated within 2-3 kpc of the galactic center during the peak accretion. With our purely thermal AGN feedback model — standard in previous literature — the outflowing material is mostly hot (10^6 K) and diffuse (nH<10^(-2) cm-3), but includes a cold component entrained in the hot wind. Despite the powerful bursts and outflow rates near the star formation rate, AGN feedback has little effect on the dense gas in the galaxy disk.

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J. Gabor and F. Bournaud
Thu, 20 Feb 14
43/52

General analytic predictions of two-field inflation and perturbative reheating [CEA]

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http://arxiv.org/abs/1402.4800


The observational signatures of multi-field inflation will generally evolve as the Universe reheats. We introduce a general analytic formalism for tracking this evolution through perturbative reheating, applicable to two field models with arbitrary separable potentials. The various transitions, including the onset of scalar field oscillations and the reheating of each field, can happen in different orders and on arbitrary hypersurfaces. The effective equations of state of the oscillating fields are also arbitrary. Nevertheless, our results are surprisingly simple. Our formalism encapsulates and generalises a huge range of previous calculations including two-field inflation, spectator models, the inhomogeneous end of inflation scenario and numerous generalised curvaton scenarios.

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J. Elliston, S. Orani and D. Mulryne
Thu, 20 Feb 14
49/52

The X-ray Properties of Weak Lensing Selected Galaxy Clusters [CEA]

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http://arxiv.org/abs/1402.4484


We present the results of an X-ray follow-up campaign targeting 10 Weak Lensing (WL) selected galaxy clusters from a Subaru WL survey. Eight clusters were studied with dedicated Chandra pointings, whereas archival X-ray data were used for the remaining two clusters. The WL clusters appear to fit the same scaling relation between X-ray luminosity and temperature as X-ray selected clusters. However, when we consider the luminosity-mass relation, the WL selected clusters appear underluminous by a factor 3.9$\pm$0.9 (or, alternatively, more massive by 2.9$\pm$0.2), compared to X-ray selected clusters. Only by considering various observational effects that could potentially bias WL masses, can this difference be reconciled. We used X-ray imaging data to quantify the dynamical state of the clusters and found that one of the clusters appears dynamically relaxed, and two of the clusters host a cool core, consistent with Sunyaev-Zel’dovich effect selected clusters. Our results suggest that regular, cool core clusters may be over-represented in X-ray selected samples.

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P. Giles, B. Maughan, T. Hamana, et. al.
Thu, 20 Feb 14
52/52

A new analysis of quasar polarisation alignments [CEA]

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http://arxiv.org/abs/1402.4313


We propose a new method to analyse the alignment of optical polarisation vectors from quasars. This method allows a precise determination of the deviation from a random distribution, and defines intrinsic preferred axes. The global significance of the effect is found to be as low as 0.003%.

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V. Pelgrims and J. Cudell
Wed, 19 Feb 14
1/50

WINGS-SPE III: Equivalent width measurements, spectral properties and evolution of local cluster galaxies [CEA]

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http://arxiv.org/abs/1402.4131


[Abridged] We investigate the frequency of the various spectral types as a function both of the clusters’ properties and of the galaxies’ characteristics. In this way, using the same classification criteria adopted for higher redshift studies, we can consistently compare the properties of the local cluster population to those of their more distant counterparts. We describe a method we have developed to automatically measure the equivalent width of spectral lines in a robust way even in spectra with a non optimal signal to noise. Like this, we can derive a spectral classification reflecting the stellar content, based on the presence and strength of the [OII] and Hdelta lines. We are able to measure 4381 of the ~6000 originally observed spectra, in the fields of 48 clusters, 2744 of which are spectroscopically confirmed cluster members. The spectral classification is then analyzed as a function of galaxies’ luminosity, stellar mass, morphology, local density and host cluster’s global properties, and compared to higher redshift samples (MORPHS and EDisCS). The vast majority of galaxies in the local clusters population are passive objects, being also the most luminous and massive. At a magnitude limit of Mv<-18, galaxies in a post-starburst phase represent only ~11% of the cluster population and this fraction is reduced to ~5% at Mv<-19.5, which compares to the 18% at the same magnitude limit for high-z clusters. “Normal” star forming galaxies [e( c )] are proportionally more common in local clusters. The relative occurrence of post–starbursts suggests a very similar quenching efficiency in clusters at redshifts in the 0 to ~1 range. Furthermore, more important than the global environment, the local density seems to be the main driver of galaxy evolution in local clusters, at least with respect to their stellar populations content.

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J. Fritz, B. Poggianti, A. Cava, et. al.
Wed, 19 Feb 14
2/50

The Dynamic Age of Centaurus A [GA]

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http://arxiv.org/abs/1402.4166


In this paper I present dynamic models of the radio source Centaurus A, and critique possible models of in situ particle reacceleration (ISR) within the radio lobes. The radio and gamma-ray data require neither homogeneous plasma nor quasi-equipartition between plasma and magnetic field; inhomogeneous models containing both high-field and low-field regions are equally likely. Cen A cannot be as young as the radiative lifetimes of its relativistic electrons, which range from a few to several tens of Myr. Two classes of dynamic models — flow driven and magnetically driven — are consistent with current observations; each requires Cen A to be on the order of a Gyr old. Thus, ongoing ISR must be occurring within the radio source. Alfven-wave ISR is probably occurring throughout the source, and may be responsible for maintaining the gamma-ray-loud electrons. It is likely to be supplemented by shock or reconnection ISR which maintains the radio-loud electrons in high-field regions.

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J. Eilek
Wed, 19 Feb 14
7/50

Low redshift quasars in the SDSS Stripe 82. The host galaxies [GA]

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http://arxiv.org/abs/1402.4300


We present a photometrical and morphological study of the properties of low redshift (z < 0.5) quasars based on a large and homogeneous dataset of objects derived from the Sloan Digital Sky Survey (DR7). This study over number by a factor about 5 any other previous study of QSO host galaxies at low redshift undertaken either on ground or on space surveys. We used about 400 quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. For these quasars we undertake a study of the host galaxies and of their environments. In this paper we report the results for the quasar hosts. We are able to detect the host galaxy for more than 3/4 of the whole dataset and characterise the properties of their hosts. We found that QSO hosts are dominated by luminous galaxies of absolute magnitude M*-3 < M(R) < M*. For the unresolved objects we computed a upper limit to the host luminosity. For each well resolved quasar we are also able to characterise the morphology of the host galaxy that turn out to be more complex than what found in previous studies. QSO are hosted in a variety of galaxies from pure ellipticals to complex/composite morphologies that combine spheroids, disk, lens and halo. The black hole mass of the quasar, estimated from the spectral properties of the nuclei, are poorly correlated with the total luminosity of the host galaxy. However, taking into account only the bulge component we found a significant correlation between the BH mass and the bulge luminosity of the host.

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R. Falomo, D. Bettoni, K. Karhunen, et. al.
Wed, 19 Feb 14
8/50

Mass-Galaxy offsets in Abell 3827, 2218 and 1689: intrinsic properties or line-of-sight substructures? [CEA]

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http://arxiv.org/abs/1402.4217


We have made mass maps of three strong-lensing clusters, Abell 3827, Abell 2218 and Abell 1689, in order to test for mass-light offsets. The technique used is GRALE, which enables lens reconstruction with minimal assumptions, and specifically with no information about the cluster light being given. In the first two of these clusters, we find local mass peaks in the central regions that are displaced from the nearby galaxies by a few to several kpc. These offsets {\em could\/} be due to line of sight structure unrelated to the clusters, but that is very unlikely, given the typical levels of chance line-of-sight coincidences in $\Lambda CDM$ simulations — for Abell 3827 and Abell 2218 the offsets appear to be intrinsic. In the case of Abell 1689, we see no significant offsets in the central region, but we do detect a possible line of sight structure: it appears only when sources at $z\ga 3$ are used for reconstructing the mass. We discuss possible origins of the mass-galaxy offsets in Abell 3827 and Abell 2218: these include pure gravitational effects like dynamical friction, but also non-standard mechanisms like self-interacting dark-matter.

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I. Mohammed, J. Liesenborgs, P. Saha, et. al.
Wed, 19 Feb 14
10/50

Dark-matter halo mergers as a fertile environment for low-mass Population III star formation [CEA]

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http://arxiv.org/abs/1402.4403


While Population III stars are typically thought to be massive, pathways towards lower-mass Pop III stars may exist when the cooling of the gas is particularly enhanced. A possible route is enhanced HD cooling during the merging of dark-matter halos. The mergers can lead to a high ionization degree catalysing the formation of HD molecules and may cool the gas down to the cosmic microwave background (CMB) temperature. In this paper, we investigate the merging of mini-halos with masses of a few 10$^5$~M$_\odot$ and explore the feasibility of this scenario. We have performed three-dimensional cosmological hydrodynamics calculations with the ENZO code, solving the thermal and chemical evolution of the gas by employing the astrochemistry package KROME. Our results show that the HD abundance is increased by two orders of magnitude compared to the no-merging case and the halo cools down to $\sim$60 K triggering fragmentation. Based on Jeans estimates the expected stellar masses are about 10 M$_\odot$. Our findings show that the merging scenario is a potential pathway for the formation of low-mass stars.

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S. Bovino, M. Latif, T. Grassi, et. al.
Wed, 19 Feb 14
13/50

Dynamics of Linear Perturbations in the hybrid metric-Palatini gravity [CEA]

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http://arxiv.org/abs/1402.4458


In this work we focus on the evolution of the linear perturbations in the novel hybrid metric-Palatini theory achieved by adding a $f(\mathcal{R})$ function to the gravitational action. Working in the Jordan frame, we derive the full set of linearized evolution equations for the perturbed potentials and present them in the Newtonian and synchronous gauges. We also derive the Poisson equation, and perform the evolution of the lensing potential, $\Phi_{+}$, for a model with a background evolution indistinguishable from $\Lambda$CDM. In order to do so, we introduce a designer approach that allows to retrieve a family of functions $f(\mathcal{R})$ for which the effective equation of state is exactly $w_{\textrm{eff}} = -1$. We conclude, for this particular model, that the main deviations from standard General Relativity and the Cosmological Constant model arise in the distant past, with an oscillatory signature in the ratio between the Newtonian potentials, $\Phi$ and $\Psi$.

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N. Lima
Wed, 19 Feb 14
14/50

A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images [CEA]

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http://arxiv.org/abs/1402.4170


Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed an exceptional number of strongly lensed multiply-imaged galaxies, including high-redshift candidates. Previous studies have used this data to obtain the most detailed dark matter reconstructions of any galaxy cluster to date, resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter, A1689) non-parametrically, combining strongly lensed images and weak distortions from wider field Subaru imaging, and we incorporate member galaxies to improve the lens solution. Strongly lensed galaxies are often locally affected by member galaxies, however, these perturbations cannot be recovered in grid based reconstructions because the lensing information is too sparse to resolve member galaxies. By adding luminosity-scaled member galaxy deflections to our smooth grid we can derive meaningful solutions with sufficient accuracy to permit the identification of our own strongly lensed images, so our model becomes self consistent. We identify 11 new multiply lensed system candidates and clarify previously ambiguous cases, in the deepest optical and NIR data to date from Hubble and Subaru. Our improved spatial resolution brings up new features not seen when the weak and strong lensing effects are used separately, including clumps and filamentary dark matter around the main halo. Our treatment means we can obtain an objective mass ratio between the cluster and galaxy components, for examining the extent of tidal stripping of the luminous member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond region. Our model independence means we can objectively evaluate the competitiveness of stacking cluster lenses for defining the geometric lensing-distance-redshift relation in a model independent way.

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J. Diego, T. Broadhurst, N. Benitez, et. al.
Wed, 19 Feb 14
16/50

Chemical enrichment by SNIa in hydrodynamical simulations -I. The Single Degenerate Scenario [GA]

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http://arxiv.org/abs/1402.4137


The nature of the Type Ia supernovae (SNIa) progenitors remains still uncertain. This is a major issue for galaxy evolution models since both chemical and energetic feedbacks play a major role in the gas dynamics, the star formation and hence, in the overall stellar evolution. The progenitor models for the SNIa available in the literature propose different distributions for regulating the explosion times of these events. These functions are known as the Delay Time Distributions (DTDs). This work is the first one of a series of papers aiming at studying five different DTDs for SNIa. Here, we implement and analyse the Single Degenerate scenario (SD) and the behaviour of the parameter A which determines the fraction of binary systems in one stellar generation that give rise to SNIa events. It worth nothing that in SPH simulations, the parameter A acts at a particle basis which has no a priori knowledge of the type of galaxy it inhabits. We determine a value of A which reproduces the [{\alpha}/Fe] ratios and the present time observed SNIa rate for a pre-prepared galaxy in isolation. The calibrated SD scenario is found to generate naturally a correlation between the specific SNIa rate and the specific SFR (SSFR) which resembles closely the observational trends. Our results suggest that SNIa observations of very low and very high SSFR of galaxies could help to set more stringent constraints on the DTDs. In a forthcoming paper, we discuss the results of five different DTDs using the same numerical approach.

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N. Jimenez, P. Tissera and F. Matteucci
Wed, 19 Feb 14
20/50

Perseus I and the NGC 3109 association in the context of the Local Group dwarf galaxy structures [GA]

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http://arxiv.org/abs/1402.4130


The recently discovered dwarf galaxy Perseus I appears to be associated with the dominant plane of non-satellite galaxies in the Local Group (LG). We predict its velocity dispersion and those of the other isolated dSphs Cetus and Tucana to be 6.5, 8.2, and 5.5 km/s, respectively. The NGC 3109 association, including the recently discovered dwarf galaxy Leo P, aligns with the dwarf galaxy structures in the LG such that all known nearby non-satellite galaxies in the northern Galactic hemisphere lie in a common thin plane (rms height 53 kpc; diameter 1.2 Mpc). This plane has an orientation similar to the preferred orbital plane of the Milky Way (MW) satellites in the vast polar structure. Five of seven of these northern galaxies were identified as possible backsplash objects, even though only about one is expected from cosmological simulations. This may pose a problem, or instead the search for local backsplash galaxies might be identifying ancient tidal dwarf galaxies expelled in a past major galaxy encounter. The NGC 3109 association supports the notion that material preferentially falls towards the MW from the Galactic south and recedes towards the north, as if the MW were moving through a stream of dwarf galaxies.

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M. Pawlowski and S. McGaugh
Wed, 19 Feb 14
22/50

Non-linear relativistic contributions to the cosmological weak-lensing convergence [CL]

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http://arxiv.org/abs/1402.4350


Relativistic contributions to the dynamics of structure formation come in a variety of forms, and can potentially give corrections to the standard picture on typical scales of 100 Mpc. These corrections cannot be obtained by Newtonian numerical simulations, so it is important to accurately estimate the magnitude of these relativistic effects. Density fluctuations couple to produce a background of gravitational waves, which is larger than any primordial background. A similar interaction produces a much larger spectrum of vector modes which represent the frame-dragging rotation of spacetime. These can change the metric at the percent level in the concordance model at scales below the equality scale. Vector modes modify the lensing of background galaxies by large-scale structure. This gives in principle the exciting possibility of measuring relativistic frame dragging effects on cosmological scales. The effects of the non-linear tensor and vector modes on the cosmic convergence are computed and compared to first-order lensing contributions from density fluctuations, Doppler lensing, and smaller Sachs-Wolfe effects. The lensing from gravitational waves is negligible so we concentrate on the vector modes. We show the relative importance of this for future surveys such as Euclid and SKA. We find that these non-linear effects only marginally affect the overall weak lensing signal so they can safely be neglected in most analyses, though are still much larger than the linear Sachs-Wolfe terms. The second-order vector contribution can dominate the first-order Doppler lensing term at moderate redshifts and are actually more important for survey geometries like the SKA.

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S. Andrianomena, C. Clarkson, P. Patel, et. al.
Wed, 19 Feb 14
23/50

Discovery of large-scale diffuse radio emission and of a new galaxy cluster in the surroundings of MACSJ0520.7-1328 [CEA]

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http://arxiv.org/abs/1402.4436


We report the discovery of large-scale diffuse radio emission South-East of the galaxy cluster MACS J0520.7-1328, detected through high sensitivity Giant Metrewave Radio Telescope 323 MHz observations. This emission is dominated by an elongated diffuse radio source and surrounded by other features of lower surface brightness. Patches of these faint sources are marginally detected in a 1.4 GHz image obtained through a re-analysis of archival NVSS data. Interestingly, the elongated radio source coincides with a previously unclassified extended X-ray source. We perform a multi-wavelength analysis based on archival infrared, optical and X-ray Chandra data. We find that this source is a low-temperature (~3.6 keV) cluster of galaxies, with indications of a disturbed dynamical state, located at a redshift that is consistent with the one of the main galaxy cluster MACS J0520.7-132 (z=0.336). We suggest that the diffuse radio emission is associated with the non-thermal components in the intracluster and intergalactic medium in and around the newly detected cluster. We are planning deeper multi-wavelength and multi-frequency radio observations to accurately investigate the dynamical scenario of the two clusters and to address more precisely the nature of the complex radio emission.

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G. Macario, H. Intema, C. Ferrari, et. al.
Wed, 19 Feb 14
25/50

X-ray AGN in the XMM-LSS galaxy clusters: no evidence for AGN suppression [CEA]

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http://arxiv.org/abs/1402.4136


We present a study of the overdensity of X-ray selected AGN in 33 galaxy clusters in the XMM-LSS field, up to redhift z=1.05. Previous studies have shown that the presence of X-ray selected AGN in rich galaxy clusters is suppressed. In the current study we investigate the occurrence of X-ray selected AGN in low and moderate X-ray luminosity galaxy clusters. Due to the wide contiguous XMM-LSS survey area we are able to extend the study to the cluster outskirts. We therefore determine the projected overdensity of X-ray point-like sources out to 6r_{500} radius. To provide robust statistical results we also use a stacking analysis of the cluster projected overdensities. We investigate whether the observed X-ray overdensities are to be expected by estimating also the corresponding optical galaxy overdensities. We find a positive X-ray projected overdensity at the first radial bin, which is however of the same amplitude as that of optical galaxies. Therefore, no suppression of X-ray AGN activity with respect to the field is found, implying that the mechanisms responsible for the suppression are not so effective in lower density environments. After a drop to roughly the background level between 2 and 3r_{500}, the X-ray overdensity exhibits a rise at larger radii, significantly larger than the corresponding optical overdensity. Finally, using redshift information of all optical counterparts, we derive the spatial overdensity profile of the clusters. We find that the agreement between X-ray and optical overdensities in the first radial bin is also suggested in the 3-dimensional analysis. However, we argue that the X-ray overdensity “bump” at larger radial distance is probably a result of flux boosting by gravitational lensing of background QSOs. For high redshift clusters an enhancement of X-ray AGN activity in their outskirts is still possible.

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E. Koulouridis, M. Plionis, O. Melnyk, et. al.
Wed, 19 Feb 14
26/50

Starobinsky-like inflation from induced gravity [CL]

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http://arxiv.org/abs/1402.2129


We derive a general criterion that defines all single-field models leading to Starobinsky-like inflation and to universal predictions for the spectral index and tensor-to-scalar ratio, which are in agreement with Planck data. Out of all the theories that satisfy this criterion, we single out a special class of models with the interesting property of retaining perturbative unitarity up to the Planck scale. These models are based on induced gravity, with the Planck mass determined by the vacuum expectation value of the inflaton.

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G. Giudice and H. Lee
Wed, 19 Feb 14
28/50

Radio-Optical Reference Frame Link Using the US Naval Observatory Astrograph and Deep CCD Imaging [IMA]

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http://arxiv.org/abs/1402.4427


Between 1997 and 2004 several observing runs were conducted mainly with the CTIO 0.9 m to image ICRF counterparts (mostly QSOs) in order to determine accurate optical positions. Contemporary to these deep CCD images the same fields were observed with the US Naval Observatory (USNO) astrograph in the same bandpass. They provide accurate positions on the Hipparcos/Tycho-2 system for stars in the 10 to 16 magnitude range used as reference stars for the deep CCD imaging data. Here we present final optical position results of 413 sources based on reference stars obtained by dedicated astrograph observations which were reduced following 2 different procedures. These optical positions are compared to radio VLBI positions. The current optical system is not perfectly aligned to the ICRF radio system with rigid body rotation angles of 3 to 5 mas (= 3 sigma level) found between them for all 3 axes. Furthermore, statistically, the optical minus radio position differences are found to exceed the total, combined, known errors in the observations. Systematic errors in the optical reference star positions as well as physical offsets between the centers of optical and radio emissions are both identified as likely causes. A detrimental, astrophysical, random noise (DARN) component is postulated to be on about the 10 mas level. If confirmed by future observations, this could severely limit the Gaia to ICRF reference frame alignment accuracy to an error of about 0.5 mas per coordinate axis with the current number of sources envisioned to provide the link. A list of 36 ICRF sources without the detection of an optical counterpart to a limiting magnitude of about R=22 is provided as well.

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N. Zacharias and M. Zacharias
Wed, 19 Feb 14
30/50

Chandra Survey of Nearby Highly Inclined Disc Galaxies – III: Comparison with Hydrodynamical Simulations of Circumgalactic Coronae [CEA]

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http://arxiv.org/abs/1402.4471


X-ray observations of circumgalactic coronae provide a valuable means by which to test galaxy formation theories. Two primary mechanisms are thought to be responsible for the establishment of such coronae: accretion of intergalactic gas (IGM) and/or galactic feedback. In this paper, we first compare our Chandra sample of galactic coronae of 53 nearby highly-inclined disc galaxies to an analytical model considering only the accretion of IGM. We confirm the existing conclusion that this pure accretion model substantially over-predicts the coronal emission. We then select 30 field galaxies from our original sample, and correct their coronal luminosities to uniformly compare them to deep X-ray measurements of several massive disc galaxies from the literature, as well as to a comparable sample of simulated galaxies drawn from the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC). These simulations explicitly model both accretion and SNe feedback and yield galaxies exhibit X-ray properties in broad agreement with our observational sample. However, notable and potentially instructive discrepancies exist between the slope and scatter of the Lx-M200 and Lx-SFR relations, highlighting some known shortcomings of GIMIC, e.g., the absence of AGN feedback, and possibly the adoption of constant stellar feedback parameters. The simulated galaxies exhibit a tight Lx-M200 correlation with little scatter. Having inferred M200 for our observational sample via the Tully-Fisher relation, we find a weaker and more scattered correlation. In the simulated and observed samples alike, massive non-starburst galaxies above a typical transition mass of M*~2e11Msun or M200~1e13Msun tend to have higher Lx/M* and Lx/M200 than low-mass counterparts, indicating that the accretion of IGM plays an increasingly important role in establishing the observable hot circumgalactic medium with increasing galaxy mass.

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J. Li, R. Crain and Q. Wang
Wed, 19 Feb 14
31/50

Possible Evidence for Metal Accretion onto the Surfaces of Metal-Poor Main-Sequence Stars [GA]

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http://arxiv.org/abs/1402.4251


The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way’s formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parametrized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

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K. Hattori, Y. Yoshii, T. Beers, et. al.
Wed, 19 Feb 14
33/50

A Riccati equation based approach to isotropic scalar field cosmologies with arbitrary self-interaction potentials [CL]

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http://arxiv.org/abs/1402.4363


Gravitationally coupled scalar fields $\phi $, distinguished by the choice of an effective self-interaction potential $V(\phi )$, simulating a temporarily non-vanishing cosmological term, can generate both inflation and late time acceleration. In scalar field cosmological models the evolution of the Hubble function is determined, in terms of the interaction potential, by a Riccati type equation. In the present work we investigate scalar field cosmological models that can be obtained as solutions of the Riccati evolution equation for the Hubble function. Four exact integrability cases of the field equations are presented, representing classes of general solutions of the Riccati evolution equation, and their cosmological properties are investigated in detail.

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T. Harko, F. Lobo and M. Mak
Wed, 19 Feb 14
38/50

Galaxy And Mass Assembly (GAMA): Testing galaxy formation models through the most massive galaxies in the Universe [CEA]

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http://arxiv.org/abs/1402.4139


We have analysed the growth of Brightest Group Galaxies and Brightest Cluster Galaxies (BGGs/BCGs) over the last 3 billion years using a large sample of 883 galaxies from the Galaxy And Mass Assembly Survey. By comparing the stellar mass of BGGs and BCGs in groups and clusters of similar dynamical masses, we find no significant growth between redshift $z=0.27$ and $z=0.09$. We also examine the number of BGGs/BCGs that have line emission, finding that approximately 65 per cent of BGGs/BCGs show H$\alpha$ in emission. From the galaxies where the necessary spectroscopic lines were accurately recovered (54 per cent of the sample), we find that half of this (i.e. 27 per cent of the sample) harbour on-going star formation with rates up to $10\,$M$_{\odot}$yr$^{-1}$, and the other half (i.e. 27 per cent of the sample) have an active nucleus (AGN) at the centre. BGGs are more likely to have ongoing star formation, while BCGs show a higher fraction of AGN activity. By examining the position of the BGGs/BCGs with respect to their host dark matter halo we find that around 13 per cent of them do not lie at the centre of the dark matter halo. This could be an indicator of recent cluster-cluster mergers. We conclude that BGGs and BCGs acquired their stellar mass rapidly at higher redshifts as predicted by semi-analytic models, mildly slowing down at low redshifts.

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P. Oliva-Altamirano, S. Brough, C. Lidman, et. al.
Wed, 19 Feb 14
41/50

The Giant Gemini GMOS survey of z>4.4 quasars – I. Measuring the mean free path across cosmic time [CEA]

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http://arxiv.org/abs/1402.4154


We have obtained spectra of 163 quasars at $z_\mathrm{em}>4.4$ with the Gemini Multi Object Spectrometers on the Gemini North and South telescopes, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this homogeneous data set, we generated stacked quasar spectra in three redshift intervals at $z\sim 5$. We have modelled the flux below the rest-frame Lyman limit ($\lambda_\mathrm{r}<912$\AA) to assess the mean free path $\lambda_\mathrm{mfp}^{912}$ of the intergalactic medium to HI-ionizing radiation. At mean redshifts $z_\mathrm{q}=4.56$, 4.86 and 5.16, we measure $\lambda_\mathrm{mfp}^{912}=(22.2\pm 2.3, 15.1\pm 1.8, 10.3\pm 1.6)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with $\lambda_\mathrm{mfp}^{912}$ measurements from lower redshifts, the data are well modelled by a simple power-law $\lambda_\mathrm{mfp}^{912}=A[(1+z)/5]^\eta$ with $A=(37\pm 2)h_{70}^{-1}$ Mpc and $\eta = -5.4\pm 0.4$ between $z=2.3$ and $z=5.5$. This rapid evolution requires a physical mechanism — beyond cosmological expansion — which reduces the cosmic effective Lyman limit opacity. We speculate that the majority of HI Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density (and consequently neutral fraction) decreases with cosmic time. Our measurements of the strongly redshift-dependent mean free path shortly after the completion of HI reionization serve as a valuable boundary condition for numerical models thereof. Having measured $\lambda_\mathrm{mfp}^{912}\approx 10$ Mpc at $z=5.2$, we confirm that the intergalactic medium is highly ionized by that epoch and that the redshift evolution of the mean free path does not show a break that would indicate a recent end to HI reionization.

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G. Worseck, J. Prochaska, J. OMeara, et. al.
Wed, 19 Feb 14
42/50

Nonlinear effects of dark energy clustering beyond the acoustic scales [CEA]

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http://arxiv.org/abs/1402.4269


We extend the resummation method of Anselmi & Pietroni (2012) to compute the total density power spectrum in models of quintessence characterized by a vanishing speed of sound. For standard $\Lambda$CDM cosmologies, this resummation scheme allows predictions with an accuracy at the few percent level beyond the range of scales where acoustic oscillations are present, therefore comparable to other, common numerical tools. In addition, our theoretical approach indicates an approximate but valuable and simple relation between the power spectra for standard quintessence models and models where scalar field perturbations appear at all scales. This, in turn, provides an educated guess for the prediction of nonlinear growth in models with generic speed of sound, particularly valuable since no numerical results are yet available.

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S. Anselmi, D. Nacir and E. Sefusatti
Wed, 19 Feb 14
43/50

Two-Dimensional Simulations of Pulsational Pair-Instability Supernovae [HEAP]

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http://arxiv.org/abs/1402.4134


Massive stars that end their lives with helium cores in the range of 35 to 65 Msun are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several times 10$^{50}$ erg each. Collisions between these shells can sometimes produce very luminous transients that are visible from the edge of the observable universe. Previous 1D studies of these events produce thin, high-density shells as one ejection plows into another. Here, in the first multidimensional simulations of these collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high density spike and drives mixing between the shells. The progenitor is a 110 Msun solar-metallicity star that was shown in earlier work to produce a superluminous supernova. The light curve of this more realistic model has a peak luminosity and duration that are similar to those of 1D models but a structure that is smoother.

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K. Chen, S. Woosley, A. Heger, et. al.
Wed, 19 Feb 14
44/50

The impact of galaxy formation on the total mass, profiles and abundance of haloes [CEA]

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http://arxiv.org/abs/1402.4461


We use cosmological hydrodynamical simulations to investigate how the inclusion of physical processes relevant to galaxy formation (star formation, metal-line cooling, stellar winds, supernovae and feedback from Active Galactic Nuclei, AGN) change the properties of haloes, over four orders of magnitude in mass. We find that gas expulsion and the associated dark matter (DM) expansion induced by supernova-driven winds are important for haloes with masses M200 < 10^13 Msun, lowering their masses by up to 20% relative to a DM-only model. AGN feedback, which is required to prevent overcooling, has a significant impact on halo masses all the way up to cluster scales (M200 ~ 10^15 Msun). Baryonic physics changes the total mass profiles of haloes out to several times the virial radius, a modification that cannot be captured by a change in the halo concentration. The decrease in the total halo mass causes a decrease in the halo mass function of about 20%. This effect can have important consequences for abundance matching technique as well as for most semi-analytic models of galaxy formation. We provide analytic fitting formulae, derived from simulations that reproduce the observed baryon fractions, to correct halo masses and mass functions from DM-only simulations. The effect of baryonic physics (AGN feedback in particular) on cluster number counts is about as large as changing the cosmology from WMAP7 to Planck, even when a moderately high mass limit of M500 ~ 10^14 Msun is adopted. Thus, for precision cosmology the effects of baryons must be accounted for.

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M. Velliscig, M. Daalen, J. Schaye, et. al.
Wed, 19 Feb 14
45/50

Detecting relic gravitational waves in the CMB: The contamination caused by the cosmological birefringence [CEA]

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http://arxiv.org/abs/1402.4324


The B-mode polarization of the cosmic microwave background (CMB) radiation is an excellent information channel for the detection of relic gravitational waves. However, the detection is contaminated by the B-mode polarization generated by some other effects. In this paper, we discuss the contaminations caused by the cosmological birefringence, which converts the CMB E-mode to the B-mode, and forms the effective noise for the detection of gravitational waves. We find that this contamination is significant, if the rotation angle is large. However, this kind of B-mode can be properly de-rotated, and the effective noises can be greatly reduced. We find that, comparing with the contaminations caused by cosmic weak lensing, the residual polarization generated by the cosmological birefringence is negligible for the detection of relic gravitational waves in the CMB.

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W. Zhao and M. Li
Wed, 19 Feb 14
46/50

The Origin and Optical Depth of Ionizing Photons in the Green Pea Galaxies [GA]

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http://arxiv.org/abs/1402.4429


Our understanding of radiative feedback and star formation in galaxies at high redshift is hindered by the rarity of similar systems at low redshift. However, the recently identified Green Pea (GP) galaxies are similar to high-redshift galaxies in their morphologies and star formation rates and are vital tools for probing the generation and transmission of ionizing photons. The GPs contain massive star clusters that emit copious amounts of high-energy radiation, as indicated by intense [OIII] 5007 emission and HeII 4686 emission. We focus on six GP galaxies with high ratios of [O III] 5007,4959/[O II] 3727 ~10 or more. Such high ratios indicate gas with a high ionization parameter or a low optical depth. The GP line ratios and ages point to chemically homogeneous massive stars, Wolf-Rayet stars, or shock ionization as the most likely sources of the He II emission. Models including shock ionization suggest that the GPs may have low optical depths, consistent with a scenario in which ionizing photons escape along passageways created by recent supernovae. The GPs and similar galaxies can shed new light on cosmic reionization by revealing how ionizing photons propagate from massive star clusters to the intergalactic medium.

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A. Jaskot and M. Oey
Wed, 19 Feb 14
47/50

The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About Reionization [CEA]

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http://arxiv.org/abs/1402.4129


[Abbreviated] We present the largest search to date for $z\sim8$ Lyman break galaxies (LBGs) based on 350 arcmin$^2$ of HST observations in the V-, Y-, J- and H-bands from the Brightest of Reionizing Galaxies (BoRG) survey. The BoRG dataset includes $\sim$50 arcmin$^2$ of new data and deeper observations of two previous BoRG pointings, from which we present 9 new $z\sim8$ LBG candidates, bringing the total number of BoRG LBGs to 38 with $25.5\leqslant m_{J} \leqslant 27.6$ (AB system). We introduce a new Bayesian formalism for estimating the galaxy luminosity function (LF), which does not require binning (and thus smearing) of the data and includes a likelihood based on the correct binomial distribution as opposed to the often used approximate Poisson distribution. We demonstrate the utility of the new method on a sample of $97$ LBGs that combines the bright BoRG galaxies with the fainter sources published in Bouwens et al. (2012) from the HUDF and ERS programs. We show that the $z\sim8$ LF is well described by a Schechter function with a characteristic magnitude $M^\star = -20.15^{+0.29}_{-0.38}$, a faint-end slope of $\alpha = -1.87^{+0.26}_{-0.26}$, and a number density of $\log_{10} \phi^\star [\textrm{Mpc}^{-3}] = -3.24^{+0.25}_{-0.24}$. Integrated down to $M=-17.7$ this LF yields a luminosity density, $\log_{10} \epsilon [\textrm{erg}/\textrm{s/Hz/Mpc}^{3}] = 25.52^{+0.05}_{-0.05}$. Our LF analysis is consistent with previously published determinations within 1$\sigma$. We discuss the implication of our study for the physics of reionization. By assuming theoretically motivated priors on the clumping factor and the photon escape fraction we show that the UV LF from galaxy samples down to $M=-17.7$ can ionize only 10-50\% of the neutral hydrogen at $z\sim8$. Full reionization would require extending the LF down to $M=-15$.

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K. Schmidt, T. Treu, M. Trenti, et. al.
Wed, 19 Feb 14
49/50

An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster [CEA]

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http://arxiv.org/abs/1402.4119


We identify a weak line at $E \sim 3.5$ keV in X-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster — two dark matter-dominated objects, for which there exist deep exposures with the XMM-Newton X-ray observatory. Such a line was not previously known to be present in the spectra of galaxies or galaxy clusters. Although the line is weak, it has a clear tendency to become stronger towards the centers of the objects; it is stronger for the Perseus cluster than for the Andromeda galaxy and is absent in the spectrum of a very deep “blank sky” dataset. Although for individual objects it is hard to exclude the possibility that the feature is due to an instrumental effect or an atomic line of anomalous brightness, it is consistent with the behavior of a line originating from the decay of dark matter particles. Future detections or non-detections of this line in multiple astrophysical targets may help to reveal its nature.

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A. Boyarsky, O. Ruchayskiy, D. Iakubovskyi, et. al.
Tue, 18 Feb 14
1/72

Bajc-Melfo Vacua enable YUMGUTs [CL]

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http://arxiv.org/abs/1402.3979


Bajc-Melfo(\textbf{BM}) two field ($S,\phi$) superpotentials define metastable F-term supersymmetry breaking vacua suitable as hidden sectors for calculable and realistic unification models. The undetermined vev $<S_s>$ of the Polonyi field that breaks Supersymmetry can be fixed either by coupling to N=1 Supergravity or by radiative corrections. \textbf{BM} hidden sectors extend to symmetric multiplets $(S,\phi)_{ab}$ of a gauged $O(N_g)$ family symmetry, broken at the GUT scale, so that the $O(N_g)$ charged component vevs $<\hat S_{ab}>$ are also undetermined before accounting for the $O(N_g)$ D-terms: which fix them by cancellation against D-term contributions from the visible sector. This facilitates Yukawon Ultra Minimal GUTs(YUMGUTs) proposed in \cite{yukawon} by relieving the visible sector from the need to give null D-terms for the family symmetry $ O(N_g)$. We analyze symmetry breaking and and spectra of the hidden sector fields in the Supergravity resolved case when $N_g=1,2,3$. Besides the Polonyi field $S_s$, most of the superfields $\hat S_{ab}$ remain light, with fermions getting masses only from loop corrections. Such modes may yield novel dark matter lighter than 100 GeV. Possible Polonyi and moduli problems associated with the the fields $S_{ab}$ call for detailed investigation of loop effects due to the Yukawa and gauge interactions in the hidden sector and of post-inflationary field relaxation dynamics.

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C. Aulakh
Tue, 18 Feb 14
3/72

The Properties of Hα Emission-Line Galaxies at $z$ = 2.24 [CEA]

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http://arxiv.org/abs/1402.3599


Using deep narrow-band $H_2S1$ and $K_{s}$-band imaging data obtained with CFHT/WIRCam, we identify a sample of 56 H$\alpha$ emission-line galaxies (ELGs) at $z=2.24$ with the 5$\sigma$ depths of $H_2S1=22.8$ and $K_{s}=24.8$ (AB) over 383 arcmin$^{2}$ area in the ECDFS. A detailed analysis is carried out with existing multi-wavelength data in this field. Three of the 56 H$\alpha$ ELGs are detected in Chandra 4 Ms X-ray observation and two of them are classified as AGNs. The rest-frame UV and optical morphologies revealed by HST/ACS and WFC3 deep images show that nearly half of the H$\alpha$ ELGs are either merging systems or with a close companion, indicating that the merging/interacting processes play a key role in regulating star formation at cosmic epoch z=2-3; About 14% are too faint to be resolved in the rest-frame UV morphology due to high dust extinction. We estimate dust extinction form SEDs. We find that dust extinction is generally correlated with H$\alpha$ luminosity and stellar mass (SM). Our results suggest that H$\alpha$ ELGs are representative of star-forming galaxies (SFGs). Applying extinction correction for individual objects, we examine the intrinsic H$\alpha$ luminosity function (LF) at $z=2.24$, obtaining a best-fit Schechter function characterized by a faint-end slope of $\alpha=-1.3$. This is shallower than the typical slope of $\alpha \sim -1.6$ in previous works based on constant extinction correction. We demonstrate that this difference is mainly due to the different extinction corrections. The proper extinction correction is thus key to recovering the intrinsic LF as the extinction globally increases with H$\alpha$ luminosity. Moreover, we find that our H$\alpha$ LF mirrors the SM function of SFGs at the same cosmic epoch. This finding indeed reflects the tight correlation between SFR and SM for the SFGs, i.e., the so-called main sequence.

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F. An, X. Zheng, W. Wang, et. al.
Tue, 18 Feb 14
4/72

A Detailed Look at the First Results from the Large Underground Xenon (LUX) Dark Matter Experiment [CL]

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http://arxiv.org/abs/1402.3731


LUX, the world’s largest dual-phase xenon time-projection chamber, with a fiducial target mass of 118 kg and 10,091 kg-days of exposure thus far, is currently the most sensitive direct dark matter search experiment. The initial null-result limit on the spin-independent WIMP-nucleon scattering cross-section was released in October 2013, with a primary scintillation threshold of 2 phe, roughly 3 keVnr for LUX. The detector has been deployed at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, and is the first experiment to achieve a limit on the WIMP cross-section lower than $10^{-45}$ cm$^{2}$. Here we present a more in-depth discussion of the novel energy scale employed to better understand the nuclear recoil light and charge yields, and of the calibration sources, including the new internal tritium source. We found the LUX data to be in conflict with low-mass WIMP signal interpretations of other results.

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M. Szydagis, D. Akerib, H. Araujo, et. al.
Tue, 18 Feb 14
8/72

Galaxy properties in clusters. II. Backsplash Galaxies [CEA]

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http://arxiv.org/abs/1402.3594


We explore the properties of galaxies on the outskirts of clusters and their dependence on recent dynamical history in order to understand the real impact that the cluster core has on the evolution of galaxies. We analyse the properties of more than 1000 galaxies brighter than $M_{^{0.1}r}$=-19.6 on the outskirts of 90 clusters ($1<r/r_{vir}<2$) in the redshift range $0.05<z<0.10$. Using the line of sight velocity, we selected high and low velocity subsamples. Theoretical predictions indicate that a significant fraction of the first subsample should be backsplash galaxies, that is, objects that have already orbited near the cluster centre. A significant proportion of the sample of high relative velocity HV galaxies seems to be composed of infalling objects. Our results suggest that, at fixed stellar mass, late type galaxies in the low velocity LV sample are systematically older, redder and have formed fewer stars during the last 3 Gyrs than galaxies in the HV sample. This result is consistent with models that assume that the central regions of clusters are effective in quenching the star formation by means of processes such as ram pressure stripping or strangulation. At fixed stellar mass, LV galaxies show some evidence of having higher surface brightness and smaller size than HV galaxies. These results are consistent with the scenario where galaxies that have orbited the central regions of clusters are more likely to suffer tidal effects, producing loss of mass as well as a redistribution of matter towards more compact configurations. Finally, we found a higher fraction of ET galaxies in the LV sample, supporting the idea that the central region of clusters of galaxies may contribute to the transformation of morphological types towards earlier types.

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H. Muriel and V. Coenda
Tue, 18 Feb 14
11/72

A Guide to Designing Future Ground-based CMB Experiments [CEA]

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http://arxiv.org/abs/1402.4108


In this follow-up work to the High Energy Physics Community Summer Study 2013 (HEP CSS 2013, a.k.a. Snowmass), we explore the scientific capabilities of a future Stage-IV Cosmic Microwave Background polarization experiment (CMB-S4) under various assumptions on detector count, resolution, and sky coverage. We use the Fisher matrix technique to calculate the expected uncertainties in cosmological parameters in $\nu \Lambda$CDM that are especially relevant to the physics of fundamental interactions, including neutrino masses, effective number of relativistic species, dark-energy equation of state, dark-matter annihilation, and inflationary parameters. To further chart the landscape of future cosmology probes, we include forecasted results from the Baryon Acoustic Oscillation (BAO) signal as measured by DESI to constrain parameters that would benefit from low redshift information. We find the following best 1-sigma constraints: $\sigma$ constraints: $\sigma(M_{\nu})= 15$ meV, $\sigma(N_{\rm eff})= 0.0156$, Dark energy Figure of Merit = 303, $\sigma(p_{ann})= 0.00588\times3\times10^{-26}$ cm$^3$/s/GeV, $\sigma(\Omega_K)= 0.00074$, $\sigma(n_s)= 0.00110$, $\sigma(\alpha_s)= 0.00145$, and $\sigma(r)= 0.00009$. We also detail the dependences of the parameter constraints on detector count, resolution, and sky coverage.

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W. Wu, J. Errard, C. Dvorkin, et. al.
Tue, 18 Feb 14
15/72

Information Gains from Cosmic Microwave Background Experiments [CEA]

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http://arxiv.org/abs/1402.3593


To shed light on the fundamental problems posed by Dark Energy and Dark Matter, a large number of experiments have been performed and combined to constrain cosmological models. We propose a novel way of quantifying the information gained by updates on the parameter constraints from a series of experiments which can either complement earlier measurements or replace them. For this purpose, we use the Kullback-Leibler divergence or relative entropy from information theory to measure differences in the posterior distributions in model parameter space from a pair of experiments. We apply this formalism to a historical series of Cosmic Microwave Background experiments ranging from Boomerang to WMAP, SPT, and Planck. Considering different combinations of these experiments, we thus estimate the information gain in units of bits and distinguish contributions from the reduction of statistical errors and the `surprise’ corresponding to a significant shift of the parameters’ central values. For this experiment series, we find individual relative entropy gains ranging from about 1 to 30 bits. In some cases, e.g. when comparing WMAP and Planck results, we find that the gains are dominated by the surprise rather than by improvements in statistical precision. We discuss how this technique provides a useful tool for both quantifying the constraining power of data from cosmological probes and detecting the tensions between experiments.

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S. Seehars, A. Amara, A. Refregier, et. al.
Tue, 18 Feb 14
16/72

Mining Circumgalactic Baryons in the Low-Redshift Universe [CEA]

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http://arxiv.org/abs/1402.3602


(Abridged) This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of a suite of absorption features including Lya, CII, CIV, SiII, SiIII, and SiIV transitions. Cross-matching between public galaxy and QSO survey data has yielded 111 independent galaxy and QSO pairs for which high-quality archival UV spectra of the QSOs and multi-wavelength observations of the galaxies are available. The galaxy sample is characterized by a median redshift of <z> = 0.0232, a median projected distance of <d> = 342 kpc, and a median stellar mass of log (Mstar/Msun) = 9.04\pm 0.93. It is therefore dominated by low-mass dwarf galaxies. Comparing the absorber features identified in the QSO spectra with galaxy properties has led to strong constraints for the CGM at z<~0.06. While abundant hydrogen gas is found beyond the dark matter halo radius Rh and all through d~500 kpc with a mean covering fraction of ~50%, no heavy elements are detected at d>~0.5 Rh. The lack of heavy elements at large distances is unlikely due to ionization effects, since it persists through all ionization states included in the study. Considering all galaxies at d>Rh leads to a strict upper limit for the covering fraction of heavy elements of ~4% (at a 95% confidence level) over d=(1-10) Rh. At d<0.5 Rh, differential covering fraction between low- and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d<0.2 Rh to larger distances. Comparing absorption-line observations of the CGM at low and high redshifts shows that massive starburst galaxies at z=2.2 exhibit significantly stronger mean absorption than dwarf galaxies at z~0 and the distinction is most pronounced in low-ionization species traced by CII and SiII absorption lines, suggesting distinct ionization conditions between the CGM at low and high redshifts.

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C. Liang and H. Chen
Tue, 18 Feb 14
19/72

Hawking Radiation from Higher-dimensional Black Holes [CL]

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http://arxiv.org/abs/1402.3952


We review the quantum field theory description of Hawking radiation from evaporating black holes and summarize what is known about Hawking radiation from black holes in more than four space-time dimensions. In the context of the Large Extra Dimensions scenario, we present the theoretical formalism for all types of emitted fields and a selection of results on the radiation spectra. A detailed analysis of the Hawking fluxes in this case is essential for modelling the evaporation of higher-dimensional black holes at the LHC, whose creation is predicted by low-energy models of quantum gravity. We discuss the status of the quest for black-hole solutions in the context of the Randall-Sundrum brane-world model and, in the absence of an exact metric, we review what is known about Hawking radiation from such black holes.

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P. Kanti and E. Winstanley
Tue, 18 Feb 14
21/72

New light on gamma-ray burst host galaxies with Herschel [GA]

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http://arxiv.org/abs/1402.4006


Until recently, dust emission has been detected in very few host galaxies of gamma-ray bursts (GRBHs). With Herschel, we have now observed 17 GRBHs up to redshift z~3 and detected seven of them at infrared (IR) wavelengths. This relatively high detection rate (41%) may be due to the composition of our sample which at a median redshift of 1.1 is dominated by the hosts of dark GRBs. Although the numbers are small, statistics suggest that dark GRBs are more likely to be detected in the IR than their optically-bright counterparts. Combining our IR data with optical, near-infrared, and radio data from our own datasets and from the literature, we have constructed spectral energy distributions (SEDs) which span up to 6 orders of magnitude in wavelength. By fitting the SEDs, we have obtained stellar masses, dust masses, star-formation rate (SFR), and extinctions for our sample galaxies. We find that GRBHs are galaxies that tend to have a high specfic SFR (sSFR), and like other star-forming galaxies, their ratios of dust-to-stellar mass are well correlated with sSFR. We incorporate our Herschel sample into a larger compilation of GRBHs, and compare this combined sample to SFR-weighted median stellar masses of the widest, deepest galaxy survey to date. This is done in order to establish whether or not GRBs can be used as an unbiased tracer of cosmic comoving SFR density (SFRD) in the universe. In contrast with previous results, this comparison shows that GRBHs are medium-sized galaxies with relatively high sSFRs; stellar masses and sSFRs of GRBHs as a function of redshift are similar to what is expected for star-forming galaxy populations at similar redshifts. We conclude that there is no strong evidence that GRBs are biased tracers of SFRD; thus they should be able to reliably probe the SFRD to early epochs.

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L. Hunt, E. Palazzi, M. Michalowski, et. al.
Tue, 18 Feb 14
23/72

Dynamical System of Scalar Field from 2-Dimension to 3-D and its Cosmological Implication [CL]

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http://arxiv.org/abs/1402.4045


We give the three-dimensional dynamical autonomous systems for most of the popular scalar field dark energy models including (phantom) quintessence, (phantom) tachyon, k-essence and general non-canonical scalar field models and change the dynamical variables from trivial variables $(x, y, \lambda)$ to observable related variables $(w_{\phi}, \Omega_{\phi}, \lambda)$. We show the intimate relationships between those scalar fields that the three-dimensional system of k-essence can reduce to (phantom) tachyon, general non-canonical scalar field can reduce to (phantom) quintessence and k-essence can also reduce to (phantom) quintessence for some special cases. For the applications of the three-dimensional dynamical systems, we investigate several special cases and give the exactly dynamical solutions in detail. Furthermore, we proved that the dark energy density parameter $\Omega_{\phi}$ would obey the same differential equation not only for all the scalar models in this paper but also for all the non-coupled dark energy models under the GR frame. We therefore get the result that, if we want to find a dark energy phenomenological model which possesses a stable attractor corresponding to current universe with $\Omega_{de}\sim 0.70$ and $\gamma_{de}\sim 0.1$ to solve or at least alleviate the cosmological coincidence problem without fine-tunings, we must consider the interaction between dark energy and other barotropic fluids. This result is valid for not only all the non-coupled dark energy models, but also for many modified gravity models as long as the energy density and the pressure of dark energy (or effective dark energy) satisfies the continuity equation in Eq.(67). In the end of this paper, we also raise a question about the possibility of the chaotic behavior in the spatially flat single scalar field FRW cosmological models in the presence of ordinary matter.

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W. Fang, H. Tu, J. Huang, et. al.
Tue, 18 Feb 14
26/72

QHD, Dark Matter and Dark Energy [CL]

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http://arxiv.org/abs/1402.4106


In QHD the weak bosons, quarks and leptons are bound states of fundamental constituents, denoted as haplons. The confinement scale of the associated gauge group SU(2)_h is of the order of $\Lambda_h\simeq 0.3$ TeV. One scalar state has zero haplon number and is the resonance observed at the LHC. In addition, there exist new bound states of haplons with no counterpart in the SM, having a mass of the order of 0.5 TeV up to a few TeV. In particular, a neutral scalar state with haplon number 4 is stable and can provide the dark matter in the universe. The QHD, QCD and QED couplings can unify at the Planck scale. If this scale changes slowly with cosmic time, all of the fundamental couplings, the masses of the nucleons and of the DM particles, including the cosmological term (or vacuum energy density), will evolve with time. This could explain the dark energy of the universe.

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H. Fritzsch and J. Sola
Tue, 18 Feb 14
27/72

Dust Spectral Energy Distributions of Nearby Galaxies: an Insight from the Herschel Reference Survey [GA]

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http://arxiv.org/abs/1402.3597


We gather infrared (IR) photometric data from 8 to 500 microns (Spitzer, WISE, IRAS and Herschel) for all of the HRS galaxies. Draine & Li (2007) models are fit to the data from which the stellar contribution has been carefully removed. We find that our photometric coverage is sufficient to constrain all of the models parameters and that a strong constraint on the 20-60 microns range is mandatory to estimate the relative contribution of the photo-dissociation regions to the IR SED. The SED models tend to systematically under-estimate the observed 500 microns flux densities, especially for low mass systems. We provide the output parameters for all of the galaxies: the minimum intensity of the interstellar radiation field (ISRF), the fraction of PAH, the relative contribution of PDR and evolved stellar population to the dust heating, the $M_{dust}$ and the $L_{IR}$. For a subsample of gas-rich galaxies, we analyze the relations between these parameters and the integrated properties of galaxies, such as $M_*$, SFR, metallicity, H$\alpha$ and H-band surface brightness, and the FUV attenuation. A good correlation between the fraction of PAH and the metallicity is found implying a weakening of the PAH emission in galaxies with low metallicities. The intensity of the IRSF and the H-band and H$\alpha$ surface brightnesses are correlated, suggesting that the diffuse dust component is heated by both the young stars in star forming regions and the diffuse evolved population. We use these results to provide a new set of IR templates calibrated with Herschel observations on nearby galaxies and a mean SED template to provide the z=0 reference for cosmological studies. For the same purpose, we put our sample on the SFR-$M_*$ diagram. The templates are compared to the most popular IR SED libraries, enlightening a large discrepancy between all of them in the 20-100 microns range.

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L. Ciesla, M. Boquien, A. Boselli, et. al.
Tue, 18 Feb 14
28/72

Spectroscopic redshifts of galaxies within the Frontier Fields [CEA]

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http://arxiv.org/abs/1402.3769


We present a catalog of 1848 spectroscopic redshifts measured in the fields of the massive galaxy clusters MACSJ0416.1-2403 ($z=0.397$), MACSJ0717.5+3745 ($z=0.546$), and MACSJ1149.5+2223 ($z=0.544$), i.e., three of the four clusters selected by STScI as the targets of the Frontier Fields (FF) initiative for studies of the distant Universe via gravitational lensing. Compiled in the course of the MACS project (Massive Cluster Survey) that detected the FF clusters, this catalog is provided to the community for three purposes: (1) to allow the identification of cluster members for studies of the galaxy population of these extreme systems, (2) to facilitate the removal of unlensed galaxies and thus reduce shear dilution in weak-lensing analyses, and (3) to improve the calibration of photometric redshifts based on both ground- and spacebased observations of the FF clusters.

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H. Ebeling, C. Ma and E. Barrett
Tue, 18 Feb 14
32/72

Astrophysical and Dark Matter Interpretations of Extended Gamma Ray Emission from the Galactic Center [HEAP]

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http://arxiv.org/abs/1402.4090


We construct empirical models of the diffuse gamma-ray background toward the Galactic Center. Including all known point sources and a template of emission associated with interactions of cosmic rays with molecular gas, we show that the extended emission observed previously in the Fermi Large Area Telescope data toward the Galactic Center is detected at high significance for all permutations of the diffuse model components. However, we find that the fluxes and spectra of the sources in our model change significantly depending on the background model. In particular, the spectrum of the central Sgr A$^\ast$ source is less steep than in previous works and the recovered spectrum of the extended emission has large systematic uncertainties, especially at lower energies. If the extended emission is interpreted to be due to dark matter annihilation, we find annihilation into pure $b$-quark and $\tau$-lepton channels to be statistically equivalent goodness-of-fits. In the case of the pure $b$-quark channel, we find a dark matter mass of $39.4\left(^{+3.7}_{-2.9}\rm\ stat.\right)\left(\pm 7.9\rm\ sys.\right)\rm\ GeV$, while a pure $\tau^{+} \tau^{-}$ channel case has an estimated dark matter mass of $9.43\left(^{+0.63}_{-0.52}\rm\ stat.\right)(\pm 1.2\rm\ sys.)\ GeV$. Alternatively, if the extended emission is interpreted to be astrophysical in origin such as due to unresolved millisecond pulsars, we obtain strong bounds on dark matter annihilation, although systematic uncertainties due to the dependence on the background models are significant.

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K. Abazajian, N. Canac, S. Horiuchi, et. al.
Tue, 18 Feb 14
33/72

Spectroscopic observation of Ly$α$ emitters at z~7.7 and implications on re-ionization [CEA]

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http://arxiv.org/abs/1402.3604


We present spectroscopic follow-up observations on two bright Ly$\alpha$ emitter (LAE) candidates originally found by Krug et al. (2012) at a redshift of z~7.7 using the Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE) at Keck. We rule out any line emission at the >5$\sigma$ level for both objects, putting on solid ground a previous null result for one of the objects. The limits inferred from the non-detections rule out the previous claim of no or even reversed evolution between 5.7 < z < 7.7 in the Ly$\alpha$ luminosity function (LF) and suggest a drop in the Ly$\alpha$ luminosity function consistent with that seen in Lyman Break galaxy (LBG) samples. We model the redshift evolution of the LAE LF using the LBG UV continuum LF and the observed rest-frame equivalent width distribution. From the comparison of our empirical model with the observed LAE distribution, we estimate lower limits of the neutral hydrogen fraction to be 50-70% at z~7.7. Together with this, we find a strong evolution in the Ly$\alpha$ optical depth characterized by (1+z)^(2.2 $\pm$ 0.5) beyond z=6 indicative of a strong evolution of the IGM. Finally, we extrapolate the LAE LF to z~9 using our model and show that it is unlikely that large area surveys like UltraVISTA or Euclid pick up LAEs at this redshift assuming the current depths and area.

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A. Faisst, P. Capak, C. Carollo, et. al.
Tue, 18 Feb 14
34/72

Luminous star-forming galaxies in the SDSS-GALEX database [CEA]

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http://arxiv.org/abs/1402.4076


We use the combined photometric SDSS + GALEX database to look for populations of luminous blue star-forming galaxies. These were initially identified from such a sample at redshifts near 0.4, using SDSS spectra. We make use of the colour index previously defined to separate stars and QSOs, to locate more of these unusual galaxies, to fainter limits. They are found in significant numbers in two different regions of the related colour-magnitude plot. Within these regions, we use the ensemble 7-colour photometry to estimate the populations of blue star-forming galaxies at redshift near 0.4, and at redshift near 1, from a full photometric sample of over half a million, composed mostly of normal galaxies and QSOs.

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J. Hutchings and L. Bianchi
Tue, 18 Feb 14
35/72

VLT/X-shooter spectroscopy of the GRB 120327A afterglow [HEAP]

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http://arxiv.org/abs/1402.4026


We present a study of the environment of the Swift long gamma-ray burst GRB 120327A at z ~2.8 through optical spectroscopy of its afterglow. We analyzed medium-resolution, multi-epoch spectroscopic observations (~7000 – 12000, corresponding to ~ 15 – 23 km/s, S/N = 15- 30 and wavelength range 3000-25000AA) of the optical afterglow of GRB 120327A, taken with X-shooter at the VLT 2.13 and 27.65 hr after the GRB trigger. The first epoch spectrum shows that the ISM in the GRB host galaxy at z = 2.8145 is extremely rich in absorption features, with three components contributing to the line profiles. The hydrogen column density associated with GRB 120327A has log NH / cm^(-2) = 22.01 +/- 0.09, and the metallicity of the host galaxy is in the range [X/H] = -1.3 to -1.1. In addition to the ground state lines, we detect absorption features associated with excited states of CII, OI, SiII, FeII, and NiII, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The variability of the FeI\lambda2396 excited line between the two epochs proves that these features are excited by the GRB UV flux. Moreover, the distance of component I is found to be dI=200+100-60 pc, while component II is located closer to the GRB, at dII=100+40-30 pc. These values are among the lowest found in GRBs. Component III does not show excited transitions, so it should be located farther away from the GRB. The presence of H2 molecules is firmly established, with a molecular fraction in the range f=4 X 10^(-7) – 10^(-4). This particularly low value can be attributed to the small dust content. This represents the third positive detection of molecules in a GRB environment.

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V. DElia, J. Fynbo, P. Goldoni, et. al.
Tue, 18 Feb 14
36/72

Revealing the location and structure of the accretion disk-wind in PDS456 [HEAP]

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http://arxiv.org/abs/1402.3700


We present evidence for the rapid variability of the high velocity iron K-shell absorption in the nearby ($z=0.184$) quasar PDS456. From a recent long Suzaku observation in 2013 ($\sim1$Ms effective duration) we find that the the equivalent width of iron K absorption increases by a factor of $\sim5$ during the observation, increasing from $<105$eV within the first 100ks of the observation, towards a maximum depth of $\sim500$eV near the end. The implied outflow velocity of $\sim0.25$c is consistent with that claimed from earlier (2007, 2011) Suzaku observations. The absorption varies on time-scales as short as $\sim1$ week. We show that this variability can be equally well attributed to either (i) an increase in column density, plausibly associated with a clumpy time-variable outflow, or (ii) the decreasing ionization of a smooth homogeneous outflow which is in photo-ionization equilibrium with the local photon field. The variability allows a direct measure of absorber location, which is constrained to within $r=200-3500$$\rm{r_{g}}$ of the black hole. Even in the most conservative case the kinetic power of the outflow is $\gtrsim6\%$ of the Eddington luminosity, with a mass outflow rate in excess of $\sim40\%$ of the Eddington accretion rate. The wind momentum rate is directly equivalent to the Eddington momentum rate which suggests that the flow may have been accelerated by continuum-scattering during an episode of Eddington-limited accretion.

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J. Gofford, J. Reeves, V. Braito, et. al.
Tue, 18 Feb 14
37/72

The Broad Wing of [O III] λ5007 Emission Line in Active Galactic Nuclei [GA]

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http://arxiv.org/abs/1402.3744


We use a type 2 AGN sample from SDSS DR7 in which the [O III] {\lambda}5007 emission line can be modeled by two Gaussian components, a broad wing plus a narrow core, to investigate the origin of the broad wing and the connection between the velocity shift of the broad wing and the physical parameters of active galactic nuclei (AGNs) as well as their host galaxies. We find that the flux of the wing components is roughly equal to that of the core components in statistic. However, the velocity shift of the wing component has only weak, if any, correlations with the physical properties of AGNs and the host galaxies such as bolometric luminosity, the Eddington ratio, the mass of supermassive black holes, D4000, H{\delta}A or stellar mass. Comparing the velocity shift from our type 2 AGN sample to that from type 1 sample in Zhang et al. (2011), we suggest the [O III] broad wing originates from outflow.

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Z. Peng, Y. Chen, Q. Gu, et. al.
Tue, 18 Feb 14
38/72

Unveiling the population of high-redshift radio galaxies using centimeter GMRT survey [GA]

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http://arxiv.org/abs/1402.3996


Ultra Steep Spectrum (USS) radio sources are one of the efficient tracers of High Redshift Radio Galaxies (HzRGs). To search for HzRGs candidates, we investigate properties of a large sample of faint USS sources derived from our deep 325 MHz GMRT observations combined with 1.4 GHz VLA data on the two subfields (i.e., VLA-VIMOS VLT Deep Survey (VVDS) and Subaru X-ray Deep Field (SXDF)) in the XMM-LSS field. The available redshift estimates show that majority of our USS sample sources are at higher redshifts with the median redshifts ~ 1.18 and ~ 1.57 in the VLA-VVDS and SXDF fields. In the VLA-VVDS field, ~ 20% of USS sources lack the redshift estimates as well as the detection in the deep optical, IR surveys, and thus these sources may be considered as potential high-z candidates. The radio luminosity distributions suggest that a substantial fraction (~ 40%) of our USS sample sources are radio-loud sources, distributed over redshifts ~ 0.5 to 4.

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V. Singh, A. Beelen, Y. Wadadekar, et. al.
Tue, 18 Feb 14
39/72

The nature of [S III]λλ9096, 9532 emitters at z = 1.34 and 1.23 [GA]

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http://arxiv.org/abs/1402.3600


A study of [S III]$\lambda\lambda9096,9532$ emitters at $z$ = 1.34 and 1.23 is presented using our deep narrow-band $H_2S1$ (centered at 2.13 $\mu$m) imaging survey of the Extended Chandra Deep Field South (ECDFS). We combine our data with multi-wavelength data of ECDFS to build up spectral energy distributions (SEDs) from the $U$ to the $K_{s}$-band for emitter candidates selected with strong excess in $H_2S1 – K_{s}$ and derive photometric redshifts, line luminosities, stellar masses and extinction. A sample of 14 [S III] emitters are identified with $H_2S1<22.8$ and $K_{\rm s}<24.8$ (AB) over 381 arcmin$^{2}$ area, having [S III] line luminosity $L_{[SIII]}= \sim 10^{41.5-42.6}$erg s$^{-1}$. None of the [S III] emitters is found to have X-ray counterpart in the deepest Chandra 4 Ms observation, suggesting that they are unlikely powered by AGN. HST/ACS F606W and HST/WFC3 F160W images show their rest-frame UV and optical morphologies. About half of the [S III] emitters are mergers and at least one third are disk-type galaxies. Nearly all [S III] emitters exhibit a prominent Balmer break in their SEDs, indicating the presence of a significant post-starburst component. Taken together, our results imply that both shock heating in post-starburst and photoionization caused by young massive stars are likely to excite strong [S III] emission lines. We conclude that the emitters in our sample are dominated by star-forming galaxies with stellar mass $8.7<\log (M/M_{sun})<9.9$.

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F. An, X. Zheng, Y. Meng, et. al.
Tue, 18 Feb 14
44/72

Distance Determinations to SHIELD Galaxies from HST Imaging [GA]

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http://arxiv.org/abs/1402.3723


The Survey of HI in Extremely Low-mass Dwarf galaxies (SHIELD) is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies. The galaxies were selected from the first ~10% of the HI ALFALFA survey based on their inferred low HI mass and low baryonic mass, and all systems have recent star formation. Thus, the SHIELD sample probes the faint end of the galaxy luminosity function for star-forming galaxies. Here, we measure the distances to the 12 SHIELD galaxies to be between 5-12 Mpc by applying the tip of the red giant method to the resolved stellar populations imaged by the Hubble Space Telescope. Based on these distances, the HI masses in the sample range from $4\times10^6$ to $6\times10^7$ M$_{\odot}$, with a median HI mass of $1\times10^7$ M$_{\odot}$. The TRGB distances are up to 73% farther than flow-model estimates in the ALFALFA catalog. Because of the relatively large uncertainties of flow model distances, we are biased towards selecting galaxies from the ALFALFA catalog where the flow model underestimates the true distances. The measured distances allow for an assessment of the native environments around the sample members. Five of the galaxies are part of the NGC 672 and NGC 784 groups, which together constitute a single structure. One galaxy is part of a larger linear ensemble of 9 systems that stretches 1.6 Mpc from end to end. Two galaxies reside in regions with 1-4 neighbors, and four galaxies are truly isolated with no known system identified within a radius of 1 Mpc.

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K. McQuinn, J. Cannon, A. Dolphin, et. al.
Tue, 18 Feb 14
47/72

Cyclic universe from a new chameleon scalar field [CEA]

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http://arxiv.org/abs/1402.3863


We explore a cyclic universe by introducing a new chameleon scalar field. In the original version of chameleon scalar field, the mass of the chameleon scalar depends on the environment, specifically on the ambient matter density. But in this new version, the ambient energy density determines not its mass but its kinetic energy which is achieved by the Lagrange multiplier field. We find the new chameleon scalar is dominant both in the very early universe and in the far future of the universe such that a cyclic universe is found. In this model of universe, there are infinite cycles of expansion and contraction. Different from the inflationary universe, the corresponding cosmic space-time is geometrically complete and quantum stable. But similar to the Cyclic Model, the flatness problem, the horizon problem and the large scale structure of the universe can be explained in this cyclic universe.

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C. Gao, Y. Lu and Y. Shen
Tue, 18 Feb 14
51/72

The Age Distribution of Clusters in M83 [GA]

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http://arxiv.org/abs/1402.3595


In order to empirically determine the timescale and environmental dependence of stellar cluster disruption, we have undertaken an analysis of the unprecedented multi-pointing (seven), multi-wavelength (U, B, V, H$\alpha$, and I) Hubble Space Telescope imaging survey of the nearby, face-on spiral galaxy M83. The images are used to locate stellar clusters and stellar associations throughout the galaxy. Estimation of cluster properties (age, mass, and extinction) was done through a comparison of their spectral energy distributions with simple stellar population models. We constructed the largest catalog of stellar clusters and associations in this galaxy to-date, with ~1800 sources with masses above ~5000 M$_{\odot}$ and ages younger than ~300 Myr. In the present letter, we focus on the age distribution of the resulting clusters and associations. In particular, we explicitly test whether the age distributions are related with the ambient environment. Our results are in excellent agreement with previous studies of age distributions in the centre of the galaxy, which gives us confidence to expand out to search for similarities or differences in the other fields which sample different environments. We find that the age distribution of the clusters inside M83 varies strongly as a function of position within the galaxy, indicating a strong correlation with the galactic environment. If the age distributions are approximated as a power-law of the form $dN/dt \propto t^{\zeta}$, we find $\zeta$ values between 0 and -0.62 ( $\zeta$~-0.40 for the whole galaxy), in good agreement with previous results and theoretical predictions.

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E. Silva-Villa, A. Adamo, N. Bastian, et. al.
Tue, 18 Feb 14
53/72

The applicability of FIR fine-structure lines as Star Formation Rate tracers over wide ranges of metallicities and galaxy types [GA]

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http://arxiv.org/abs/1402.4075


We analyze the applicability of far-infrared fine-structure lines [CII] 158 micron, [OI] 63 micron and [OIII] 88 micron to reliably trace the star formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the Herschel Dwarf Galaxy Survey and compare with a broad sample of galaxies of various types and metallicities in the literature. We study the trends and scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24 micron) and far-infrared line emission, on spatially resolved and global galaxy scales, in dwarf galaxies. We assemble far-infrared line measurements from the literature and infer whether the far-infrared lines can probe the SFR (as traced by the total-infrared luminosity) in a variety of galaxy populations. In metal-poor dwarfs, the [OI] and [OIII] lines show the strongest correlation with the SFR with an accuracy on the SFR estimates better than a factor of 2, while the link between [CII] emission and the SFR is more dispersed (factor of 2.5 accuracy). The scatter in the SFR-L([CII]) relation increases towards low metal abundances, warm dust temperature, large filling factors of diffuse, highly ionized gas (high values of [OIII]/[CII]+[OI]) and high [O{\sc{i}}]$_{63}$/[CII]+[OI] line ratios. For the literature sample, we evaluate the correlations for a number of different galaxy populations. The [CII] and [OI] lines are considered to be reliable SFR tracers in starburst galaxies, recovering the star formation activity within a precision factor of 2. [Abridged]

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I. Looze, D. Cormier, V. Lebouteiller, et. al.
Tue, 18 Feb 14
54/72

Evolution of the universe in entropic cosmologies via different formulations [CEA]

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http://arxiv.org/abs/1402.3755


We study two types of entropic-force models in a homogeneous, isotropic, spatially flat, matter-dominated universe. The first type is a `$\Lambda(t)$ type’ similar to $\Lambda(t)$CDM (varying-lambda cold dark matter) models in which both the Friedmann equation and the acceleration equation include an extra driving term. The second type is a `BV type’ similar to bulk viscous models in which the acceleration equation includes an extra driving term whereas the Friedmann equation does not. In order to examine the two types systematically, we consider an extended entropic-force model that includes a Hubble parameter ($H$) term and a constant term in entropic-force terms. The $H$ term is derived from a volume entropy whereas the constant term is derived from an entropy proportional to the square of an area entropy. Based on the extended entropic-force model, we examine four models obtained from combining the $H$ and constant terms with the $\Lambda(t)$ and BV types. The four models agree well with the observed supernova data and describe the background evolution of the late universe properly. However, the evolution of first-order density perturbations is different in each of the four models, especially for low redshift. The $\Lambda(t)$ type is found to be consistent with the observed growth rate of clustering, in contrast with the BV type examined in this study.

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N. Komatsu and S. Kimura
Tue, 18 Feb 14
57/72

Self-Interacting Dark Matter from a Non-Abelian Hidden Sector [CL]

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http://arxiv.org/abs/1402.3629


There is strong evidence in favor of the idea that dark matter is self-interacting, with cross section-to-mass ratio $\sigma / m \sim 1~\mathrm{cm^2/g} \sim 1~\mathrm{barn/GeV}$. We show that viable models of dark matter with this large cross section are straightforwardly realized with non-Abelian hidden sectors. In the simplest of such models, the hidden sector is a pure gauge theory, and the dark matter is hidden glueballs with mass around 100 MeV. Alternatively, the hidden sector may be a supersymmetric pure gauge theory with a $\sim 10~\mathrm{TeV}$ gluino thermal relic. In this case, the dark matter is largely composed of glueballinos that strongly self-interact through the exchange of light glueballs. We present a unified framework that realizes both of these possibilities in anomaly-mediated supersymmetry breaking, where, depending on a few model parameters, the dark matter is either hidden glueballinos, hidden glueballs, or a mixture of the two. These models provide simple examples of multi-component dark matter, have interesting implications for particle physics and cosmology, and include cases where a sub-dominant component of dark matter may be extremely strongly self-interacting, with interesting astrophysical consequences.

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K. Boddy, J. Feng, M. Kaplinghat, et. al.
Tue, 18 Feb 14
59/72

Viscous Generalized Chaplygin Gas as a Unified Dark Fluid: Including Perturbation of Bulk Viscosity [CEA]

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http://arxiv.org/abs/1402.3669


In this paper, we continue our previous work of studying viscous generalized Chaplygin gas (VGCG) as a unified dark fluid but including the bulk viscosity perturbation. By using the currently available cosmic observational data from SNLS3, BAO, HST and recently released Planck, we gain the constraint on bulk viscosity coefficient: $\zeta_0=0.0000138_{- 0.0000105- 0.0000138- 0.0000138}^{+ 0.00000614+ 0.0000145+ 0.0000212}$ in $1, 2, 3\sigma$ regions respectively via Markov Chain Monte Carlo method. The result shows that when considering perturbation of bulk viscosity, the currently cosmic observations favor a smaller bulk viscosity coefficient.

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W. Li and L. Xu
Tue, 18 Feb 14
63/72

New results on the exotic galaxy `Speca' and discovering many more Specas with RAD@home network [GA]

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http://arxiv.org/abs/1402.3674


We present the first report on an innovative new project named “RAD@home”, a citizen-science research collaboratory built on free web-services like Facebook, Google, Skype, NASA Skyview, NED, TGSS etc.. This is the first of its kind in India, a zero-funded, zero-infrastructure, human-resource network to educate and directly involve in research, hundreds of science-educated under-graduate population of India, irrespective of their official employment and home-location with in the country. Professional international collaborators are involved in follow up observation and publication of the objects discovered by the collaboratory. We present here ten newly found candidate episodic radio galaxies, already proposed to GMRT, and ten more interesting cases which includes, bent-lobe radio galaxies located in new Mpc-scale filaments, likely tracing cosmological cluster accretion from the cosmic web. Two new Speca-like rare spiral-host large radio galaxies have also been been reported here. Early analyses from our follow up observations with the Subaru and XMM-Newton telescopes have revealed that Speca is likely a new entry to the cluster and is a fast rotating, extremely massive, star forming disk galaxy. Speca-like massive galaxies with giant radio lobes, are possibly remnants of luminous quasars in the early Universe or of first supermassive black holes with in first masssve galaxies. As discoveries of Speca-like galaxies did not require new data from big telescopes, but free archival radio-optical data, these early results demonstrate the discovery potential of RAD@home and how it can help resource-rich professionals, as well as demonstrate a model of academic-growth for resource-poor people in the underdeveloped regions via Internet.

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A. Hota, J. Croston, Y. Ohyama, et. al.
Tue, 18 Feb 14
65/72

Clustering tomography: measuring cosmological distances through angular clustering in thin redshift shells [CEA]

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http://arxiv.org/abs/1402.3590


We test the cosmological implications of studying galaxy clustering using a tomographic approach, by computing the galaxy two-point angular correlation function $\omega(\theta)$ in thin redshift shells using a spectroscopic-redshift galaxy survey. The advantages of this procedure are that it is not necessary to assume a fiducial cosmology in order to convert measured angular positions and redshifts into distances, and that it gives several (less accurate) measurements of the angular diameter distance $D_\rm{A}(z)$ instead of only one (more precise) measurement of the effective average distance $D_\rm{V}(z)$, which results in better constraints on the expansion history of the Universe. We test our model for $\omega(\theta)$ and its covariance matrix against a set of mock galaxy catalogues and show that this technique is able to extract unbiased cosmological constraints. Also, assuming the best-fit $\Lambda$CDM cosmology from the cosmic microwave background measurements from the Planck satellite, we forecast the result of applying this tomographic approach to the final Baryon Oscillation Spectroscopic Survey catalogue in combination with Planck for three flat cosmological models, and compare them with the expected results of the isotropic baryon acoustic oscillation (BAO) measurements post-reconstruction on the same galaxy catalogue combined with Planck. While BAOs are more accurate for constraining cosmological parameters for the standard $\Lambda$CDM model, the tomographic technique gives better results when we allow the dark energy equation of state $w_{DE}$ deviate from $-1$, resulting in a performance similar to BAOs in the case of a constant value of $w_{DE}$, and a significant improvement in the case of a time-dependent value of $w_{DE}$, increasing the value of the Figure-of-Merit in the $w_0-w_a$ plane by a factor of $1.4$.

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S. Salazar-Albornoz, A. Sanchez, N. Padilla, et. al.
Tue, 18 Feb 14
69/72

The distribution of polarized radio sources $>$15$μ$Jy in GOODS-N [GA]

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http://arxiv.org/abs/1402.3637


We present deep VLA observations of the polarization of radio sources in the GOODS-N field at 1.4 GHz at resolutions of 1.6″ and 10″. At 1.6″, we find that the cumulative number count distribution is N($>$p) $\sim$ 45 * (p/30$\mu$Jy)$^{-0.6}$ per square degree above a detection threshold of 14.5 $\mu$Jy. This represents a break from the steeper slopes at higher flux densities, resulting in fewer sources predicted for future surveys with the SKA and its precursors. It provides a significant challenge for using background RMs to study clusters of galaxies or individual galaxies. Most of the polarized sources are well above our detection limit, and are radio galaxies which are well-resolved even at 10″, with redshifts from $\sim$0.2 – 1.9. We determined a total polarized flux for each source by integrating the 10″ polarized intensity maps, as will be done by upcoming surveys such as POSSUM. These total polarized fluxes are a factor of 2 higher, on average, than the peak polarized flux at 1.6″; this would increase the number counts by $\sim$50% at a fixed flux level. The detected sources have rotation measures (RMs) with a characteristic rms scatter of $\sim$11$\frac{rad}{m^2}$ around the local Galactic value, after eliminating likely outliers. The median fractional polarization from all total intensity sources does not continue the trend of increasing at lower flux densities, as seen for stronger sources. The changes in the polarization characteristics seen at these low fluxes likely represent the increasing dominance of star-forming galaxies.

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L. Rudnick and F. Owen
Tue, 18 Feb 14
70/72

The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf Galaxies as Revealed by RR Lyrae Variables [GA]

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http://arxiv.org/abs/1402.3874


We present the results of our analysis of the RR Lyrae (RRL) variable stars detected in two transition-type dwarf galaxies (dTrans), ESO294-G010 and ESO410-G005 in the Sculptor group, which is known to be one of the closest neighboring galaxy groups to our Local Group. Using deep archival images from the Advanced Camera for Surveys (ACS) onboard the Hubble Space Telescope (HST), we have identified a sample of RR Lyrae candidates in both dTrans galaxies [219 RRab (RR0) and 13 RRc (RR1) variables in ESO294-G010; 225 RRab and 44 RRc stars in ESO410-G005]. The metallicities of the individual RRab stars are calculated via the period-amplitude-[Fe/H] relation derived by Alcock et al. This yields mean metallicities of <[Fe/H]>_{ESO294} = -1.77 +/- 0.03 and <[Fe/H]>_{ESO410} = -1.64 +/- 0.03. The RRL metallicity distribution functions (MDFs) are investigated further via simple chemical evolution models; these reveal the relics of the early chemical enrichment processes for these two dTrans galaxies. In the case of both galaxies, the shapes of the RRL MDFs are well-described by pre-enrichment models. This suggests two possible channels for the early chemical evolution for these Sculptor group dTrans galaxies: 1) The ancient stellar populations of our target dwarf galaxies might have formed from the star forming gas which was already enriched through “prompt initial enrichment” or an “initial nucleosynthetic spike” from the very first massive stars, or 2) this pre-enrichment state might have been achieved by the end products from more evolved systems of their nearest neighbor, NGC 55.

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S. Yang, R. Wagner-Kaiser, A. Sarajedini, et. al.
Tue, 18 Feb 14
72/72

Chemo-Archeological Downsizing in a Hierarchical Universe: Impact of a Top Heavy IGIMF [CEA]

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http://arxiv.org/abs/1402.3296


We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [a/Fe] abundance ratios and stellar mass in elliptical galaxies.We implement a new galaxy-wide stellar initial mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in the semi-analytic model SAG and evaluate its impact on the chemical evolution of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach higher [a/Fe] abundance ratios because they are characterized by more top heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass, which is a free parameter involved in the TH-IGIMF theory, is found to be as low as 5 solar masses. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF.We find that, regardless of galaxy mass, older galaxies (with formation redshifts > 2) are formed in shorter time-scales (< 2Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation, but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed stellar mass.

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I. Gargiulo, S. Cora, N. Padilla, et. al.
Mon, 17 Feb 14
2/37

Excluding the Light Dark Matter Window of a 331 Model Using LHC and Direct Dark Matter Detection Data [CL]

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http://arxiv.org/abs/1402.3271


We sift the impact of the recent Higgs precise measurements and recent direct detection results on the dark sector of an electroweak extension of the Standard Model that has a complex scalar as dark matter. We find out that the Higgs decays with a large branching ratio into dark matter particles and charged scalars when these channels are kinematically available and that WIMP-nucleon scattering cross section is quite large in the low mass dark matter regime. Therefore, gathering the data from Higgs and dark matter search we literally rule out the low WIMP mass window. Lastly, we compute the charged scalar production cross section at the LHC and comment on the possibility of detection at current and future LHC runnings.

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D. Cogollo, A. Gonzalez-Morales, F. Queiroz, et. al.
Mon, 17 Feb 14
6/37

Detection of Stacked Filament Lensing Between SDSS Luminous Red Galaxies [CEA]

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http://arxiv.org/abs/1402.3302


We search for the lensing signal of massive filaments between 220,000 pairs of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey. We use a nulling technique to remove the contribution of the LRG halos, resulting in a $10 \sigma$ detection of the filament lensing signal. We compare the measurements with halo model predictions based on a calculation of 3-point halo-halo-mass correlations. Comparing the “thick” halo model filament to a “thin” string of halos, thick filaments larger than a Mpc in width are clearly preferred by the data.

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J. Clampitt, B. Jain and M. Takada
Mon, 17 Feb 14
7/37

A Generalization of Gauge Symmetry, Fourth-Order Gauge Field Equations and Accelerated Cosmic-Expansion [CL]

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http://arxiv.org/abs/1402.3572


A generalization of the usual gauge symmetry leads to fourth-order gauge field equations, which imply a new constant force independent of distances. The force associated with the new $U_1$ gauge symmetry is repulsive among baryons. Such a constant force based on baryon charge conservation gives a field-theoretic understanding of the accelerated cosmic-expansion in the observable portion of the universe dominated by baryon galaxies. In consistent with all conservation laws and known forces, a simple rotating `dumbbell model’ of the universe is briefly discussed.

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J. Hsu
Mon, 17 Feb 14
9/37

A Keplerian-based Hamiltonian Splitting for Gravitational $N$-body Simulations [CEA]

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http://arxiv.org/abs/1402.3325


We developed a Keplerian-based Hamiltonian splitting for solving the gravitational $N$-body problem. This splitting allows us to approximate the solution of a general $N$-body problem by a composition of multiple, independently evolved $2$-body problems. While the Hamiltonian splitting is exact, we show that the composition of independent $2$-body problems results in a non-symplectic non-time-symmetric first-order map. A time-symmetric second-order map is then constructed by composing this basic first-order map with its self-adjoint. The resulting method is precise for each individual $2$-body solution and produces quick and accurate results for near-Keplerian $N$-body systems, like planetary systems or a cluster of stars that orbit a supermassive black hole. The method is also suitable for integration of $N$-body systems with intrinsic hierarchies, like a star cluster with primordial binaries. The superposition of Kepler solutions for each pair of particles makes the method excellently suited for parallel computing; we achieve $\gtrsim 64\%$ efficiency for only $8$ particles per core, but close to perfect scaling for $16384$ particles on a $128$ core distributed-memory computer. We present several implementations in \texttt{Sakura}, one of which is publicly available via the AMUSE framework.

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G. Ferrari, T. Boekholt and S. Zwart
Mon, 17 Feb 14
11/37

The Thermal Sunyaev-Zeldovich Effect of Primordial Recombination Radiation [CEA]

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http://arxiv.org/abs/1402.3505


It is well known that recombination radiation of primordial hydrogen-helium plasma leads to the distortions of the planckian spectrum shape of the cosmic microwave background radiation (CMB). We discuss the thermal Sunayev-Zeldovich (SZ) effect with taking into account primordial recombination radiation (PRR). Since in the thermal SZ effect the redistribution of the photons depends on the derivatives of the spectrum, the value of relative correction to SZ effect due to PRR significantly higher than relative corrections due to PRR in the initial spectrum.
Calculations of corrections to the thermal SZ effect due to PRR show that depending on the cluster parameters:
1) in the range of frequencies $\nu$ = 0.3 – 700 GHz where the cosmic microwave background (CMB) dominates and spectrum is very close to the planckian one the relative corrections due to PRR have an order of $10^{-9} – 10^{-6}$ of “pure” SZ effect (i.e. SZ effect for pure planckian spectrum). The difference of intensities of PRR coming from different directions (through intracluster and near intercluster medium) reaches values up to 22 mJy/ster at $\nu\simeq 337$ GHz (maximum in considered range).
2) In the range of frequencies $\nu$ = 700 – 5000 GHz where cosmic infrared background (CIB) becomes significant or even dominates the relative corrections due to PRR can reach $10^{-8}$ – $10^{-5}$ of “pure” SZ effect. Corresponding intensity difference reaches values up to 25 mJy/ster (at $\nu\simeq 1700$ GHz).
In addition we suggest a modification of the method of electron gas temperature determination using corrections of the SZ effect due to PRR. Such modification allows one to simplify the determination of the cluster electron gas temperature in comparison with known methods.

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E. Kholupenko, S. Balashev, A. Ivanchik, et. al.
Mon, 17 Feb 14
14/37

Identification of the progenitors of rich clusters and member galaxies in rapid formation at z>2 [CEA]

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http://arxiv.org/abs/1402.3568


We present the results of near-infrared spectroscopy of H-alpha emitters (HAEs) associated with two proto-clusters around radio galaxies (PKS1138-262 at z=2.2 and USS1558-003 at z=2.5) with MOIRCS on Subaru telescope. Among the HAE candidates constructed from our narrow-band imaging, we have confirmed membership of 27 and 36 HAEs for the respective proto-clusters, with a success rate of 70% of our observed targets. The large number of spectroscopically confirmed members per cluster has enabled us for the first time to reveal the detailed kinematical structures of the proto-clusters at z>2. The clusters show prominent substructures such as clumps, filaments and velocity gradient, suggesting that they are still in the midst of rapid construction to grow to rich clusters at later times. We also estimate dynamical masses of the clusters and substructures assuming their local virialization. The inferred masses (~10e+14 Msun) of the proto-cluster cores are consistent with being typical progenitors of the present-day most massive class of galaxy clusters (~10e+15 Msun) if we take into account the typical mass growth history of clusters. We then calculated the integrated star formation rates of the proto-cluster cores normalized by the dynamical masses, and compare those with lower redshift descendants. We see a marked increase of star-forming activities in the cluster cores by almost three orders of magnitude as we go back in time to 11 billion years ago and it scales as (1+z)^6.

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R. Shimakawa, T. Kodama, K. Tadaki, et. al.
Mon, 17 Feb 14
16/37

More on loops in reheating: Non-gaussianities and tensor power spectrum [CL]

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http://arxiv.org/abs/1402.3316


We consider the single field chaotic $m^2{\phi}^2$ inflationary model with a period of preheating, where the inflaton decays to another scalar field \chi\ in the parametric resonance regime. In a recent work, one of us has shown that the \chi\ modes circulating in the loops during preheating notably modify the <\zeta\zeta> correlation function. We first rederive this result using a different gauge condition hence reconfirm that superhorizon \zeta\ modes are affected by the loops in preheating. Further, we examine how \chi\ loops give rise to non-gaussianity and affect the tensor perturbations. For that, all cubic and some higher order interactions involving two \chi\ fields are determined and their contribution to the non-gaussianity parameter $f_{NL}$ and the tensor power spectrum are calculated at one loop. Our estimates for these corrections show that while a large amount of non-gaussianity can be produced during reheating, the tensor power spectrum receive moderate corrections. We observe that the loop quantum effects increase with more \chi\ fields circulating in the loops indicating that the perturbation theory might be broken down. These findings demonstrate that the loop corrections during reheating are significant and they must be taken into account for precision inflationary cosmology.

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N. Katirci, A. Kaya and M. Tarman
Mon, 17 Feb 14
18/37

Testing the equal-time angular-averaged consistency relation of the gravitational dynamics in N-body simulations [CEA]

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http://arxiv.org/abs/1402.3293


We explicitly test the equal-time consistency relation between the angular-averaged bispectrum and the power spectrum of the matter density field, employing a large suite of cosmological $N$-body simulations. This is the lowest-order version of the relations between $(\ell+n)-$point and $n-$point polyspectra, where one averages over the angles of $\ell$ soft modes. This relation depends on two wave numbers, $k’$ in the soft domain and $k$ in the hard domain. We show that it holds up to a good accuracy, when $k’/k\ll 1$ and $k’$ is in the linear regime, while the hard mode $k$ goes from linear ($0.1\,h\,\mathrm{Mpc}^{-1}$) to nonlinear ($1.0\,h\,\mathrm{Mpc}^{-1}$) scales. On scales $k\lesssim 0.4\,h\,\mathrm{Mpc}^{-1}$, we confirm the relation within a $\sim 5\%$ accuracy, even though the bispectrum can already deviate from leading-order perturbation theory by more than $30\%$. We further show that the relation extends up to nonlinear scales, $k \sim 1.0\,h\,\mathrm{Mpc}^{-1}$, within an accuracy of $\sim 10\%$.

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T. Nishimichi and P. Valageas
Mon, 17 Feb 14
21/37

Electrodynamics in an LTB scenario [CEA]

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http://arxiv.org/abs/1402.3486


In this article we analyze the electrodynamics in curved space-time in LTB metric. We calculate the most general scale factor in this inhomogeneous Universe. We also study the presence of electromagnetic field bubbles in the Universe.

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G. Fanizza and L. Tedesco
Mon, 17 Feb 14
22/37

A search for HI absorption in nearby radio galaxies using HIPASS [GA]

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http://arxiv.org/abs/1402.3530


Using archival data from the HI Parkes All Sky Survey (HIPASS) we have searched for 21 cm-line absorption in 204 nearby radio and star-forming galaxies with continuum flux densities greater than $S_{1.4} \approx 250$ mJy within the redshift range $0 < cz < 12\,000$ km s$^{-1}$. By applying a detection method based on Bayesian model comparison, we successfully detect and model absorption against the radio-loud nuclei of four galaxies, of which the Seyfert 2 galaxy 2MASX J130804201-2422581 was previously unknown. All four detections were achieved against compact radio sources, which include three active galactic nuclei (AGNs) and a nuclear starburst, exhibiting high dust and molecular gas content. Our results are consistent with the detection rate achieved by the recent ALFALFA HI absorption pilot survey by Darling et al. and we predict that the full ALFALFA survey should yield more than 3-4 times as many detections as we have achieved here. Furthermore, we predict that future all-sky surveys on the SKA precursor telescopes will be able to detect such strong absorption systems associated with type-2 AGNs at much higher redshifts, providing potential targets for detection of H$_{2}$O megamaser emission at cosmological redshifts.

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J. Allison, E. Sadler and A. Meekin
Mon, 17 Feb 14
24/37

Spectra and Drag Force of Free-Streaming Massive Neutrinos [CL]

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http://arxiv.org/abs/1402.3409


We study the present day relic neutrino distribution in the Earth frame and characterize the dependence on neutrino mass and freeze-out conditions in early Universe. We present explicitly the neutrino velocity and de Broglie wavelength distributions. We characterize the expected neutrino drag force ${\cal O}(G_F^2)$ of a spherical detector in the hard sphere scattering limit, as would be experienced by a macroscopic (millimeter sized) coherent quantum detector moving at velocity $300\pm30$ km/s in this neutrino background.

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J. Birrell and J. Rafelski
Mon, 17 Feb 14
26/37

Young Star Clusters In The Circumnuclear Region Of NGC 2110 [GA]

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http://arxiv.org/abs/1402.3339


High-resolution observations in the near infrared show star clusters around the active galactic nucleus (AGN) of the Seyfert 1 NGC2110, along with a 90 x 35 pc bar of shocked gas material around its nucleus. These are seen for the first time in our imaging and gas kinematics of the central 100pc with the Keck OSIRIS instrument with adaptive optics. Each of these clusters is 2-3 times brighter than the Arches cluster close to the centre of the Milky Way. The core star formation rate (SFR) is 0.3 M$_\odot$/yr. The photoionized gas (He I) dynamics imply an enclosed mass of 3-4 x 10$^8$ M$_\odot$. These observations demonstrate the physical linkage between AGN feedback, which triggers star formation in massive clusters, and the resulting stellar (and SNe) winds, which cause the observed [Fe II] emission and feed the black hole.

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M. Durre and J. Mould
Mon, 17 Feb 14
32/37

The connection between galaxy structure and quenching efficiency [CEA]

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http://arxiv.org/abs/1402.3394


Using data from the SDSS-DR7, including structural measurements from 2D surface brightness fits with GIM2D, we show how the fraction of quiescent galaxies depends on galaxy stellar mass $M_*$, effective radius $R_e$, fraction of $r-$band light in the bulge, $B/T$, and their status as a central or satellite galaxy at $0.01<z<0.2$. For central galaxies we confirm that the quiescent fraction depends not only on stellar mass, but also on $R_e$. The dependence is particularly strong as a function of $M_*/R_e^\alpha$, with $\alpha\sim 1.5$. This appears to be driven by a simple dependence on $B/T$ over the mass range $9 < \log(M_*/M_\odot) < 11.5$, and is qualitatively similar even if galaxies with $B/T>0.3$ are excluded. For satellite galaxies, the quiescent fraction is always larger than that of central galaxies, for any combination of $M_*$, $R_e$ and $B/T$. The quenching efficiency is not constant, but reaches a maximum of $\sim 0.7$ for galaxies with $9 < \log(M_*/M_\odot) < 9.5$ and $R_e<1$ kpc. This is the same region of parameter space in which the satellite fraction itself reaches its maximum value, suggesting that the transformation from an active central galaxy to a quiescent satellite is associated with a reduction in $R_e$ due to an increase in dominance of a bulge component.

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C. Omand, M. Balogh and B. Poggianti
Mon, 17 Feb 14
33/37

Search for non-relativistic Magnetic Monopoles with IceCube [CEA]

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http://arxiv.org/abs/1402.3460


The IceCube Neutrino Observatory is a large Cherenkov detector instrumenting $1\,\mathrm{km}^3$ of Antarctic ice. The detector can be used to search for signatures of particle physics beyond the Standard Model. Here, we describe the search for non-relativistic, magnetic monopoles as remnants of the GUT (Grand Unified Theory) era shortly after the Big Bang. These monopoles may catalyze the decay of nucleons via the Rubakov-Callan effect with a cross section suggested to be in the range of $10^{-27}\,\mathrm{cm^2}$ to $10^{-21}\,\mathrm{cm^2}$. In IceCube, the Cherenkov light from nucleon decays along the monopole trajectory would produce a characteristic hit pattern. This paper presents the results of an analysis of first data taken from May 2011 until May 2012 with a dedicated slow-particle trigger for DeepCore, a subdetector of IceCube. A second analysis provides better sensitivity for the brightest non-relativistic monopoles using data taken from May 2009 until May 2010. In both analyses no monopole signal was observed. For catalysis cross sections of $10^{-22}\,(10^{-24})\,\mathrm{cm^2}$ the flux of non-relativistic GUT monopoles is constrained up to a level of $\Phi_{90} \le 10^{-18}\,(10^{-17})\,\mathrm{cm^{-2}s^{-1}sr^{-1}}$ at a 90% confidence level, which is three orders of magnitude below the Parker bound. The limits assume a dominant decay of the proton into a positron and a neutral pion. These results improve the current best experimental limits by one to two orders of magnitude, for a wide range of assumed speeds and catalysis cross sections.

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IceCube. Collaboration, M. Aartsen, R. Abbasi, et. al.
Mon, 17 Feb 14
34/37

Determining Inclinations of Active Galactic Nuclei Via Their Narrow-Line Region Kinematics – II. Correlation With Observed Properties [GA]

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http://arxiv.org/abs/1402.3509


Active Galactic Nuclei (AGN) are axisymmetric systems to first order; their observed properties are likely strong functions of inclination with respect to our line of sight, yet the specific inclinations of all but a few AGN are generally unknown. By determining the inclinations and geometries of nearby Seyfert galaxies using the kinematics of their narrow-line regions (NLRs), and comparing them with observed properties, we find strong correlations between inclination and total hydrogen column density, infrared color, and H-beta full-width at half maximum (FWHM). These correlations provide evidence that the orientation of AGN with respect to our line of sight affects how we perceive them, beyond the Seyfert type dichotomy. They can also be used to constrain 3D models of AGN components such as the broad-line region and torus. Additionally, we find weak correlations between AGN luminosity and several modeled NLR parameters, which suggests that the NLR geometry and kinematics are dependent to some degree on the AGN’s radiation field.

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T. Fischer, D. Crenshaw, S. Kraemer, et. al.
Mon, 17 Feb 14
36/37

Interpreting the Distance Correlation COMBO-17 Results [CEA]

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http://arxiv.org/abs/1402.3230


The accurate classification of galaxies in large-sample astrophysical databases of galaxy clusters depends sensitively on the ability to distinguish between morphological types, especially at higher redshifts. This capability can be enhanced through a new statistical measure of association and correlation, called the {\it distance correlation coefficient}, which is more powerful than the classical Pearson measure of linear relationships between two variables. The distance correlation measure offers a more precise alternative to the classical measure since it is capable of detecting nonlinear relationships that may appear in astrophysical applications. We showed recently that the comparison between the distance and Pearson correlation coefficients can be used effectively to isolate potential outliers in various galaxy datasets, and this comparison has the ability to confirm the level of accuracy associated with the data. In this work, we elucidate the advantages of distance correlation when applied to large databases. We illustrate how this distance correlation measure can be used effectively as a tool to confirm nonlinear relationships between various variables in the COMBO-17 database, including the lengths of the major and minor axes, and the alternative redshift distribution. For these outlier pairs, the distance correlation coefficient is routinely higher than the Pearson coefficient since it is easier to detect nonlinear relationships with distance correlation. The V-shaped scatterplots of Pearson versus distance correlation coefficients also reveal the patterns with increasing redshift and the contributions of different galaxy types within each redshift range.

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M. Richards, D. Richards and E. Martinez-Gomez
Fri, 14 Feb 14
1/42

Evolution of perturbations and cosmological constraints in decaying dark matter models with arbitrary decay mass products [CEA]

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http://arxiv.org/abs/1402.2972


Decaying dark matter (DDM) is a candidate which can solve the discrepancies between predictions of the concordance $\Lambda$CDM model and observations at small scales such as the number counts of companion galaxies of the Milky Way and the density profile at the center of galaxies. Previous studies are limited to the cases where the decay particles are massless and/or have almost degenerate masses with that of mother particles. Here we expand the DDM models so that one can consider the DDM with arbitrary lifetime and the decay products with arbitrary masses. We calculate the time evolutions of perturbed phase-space distribution functions of decay products for the first time and study effects of DDM on the temperature anisotropy in the cosmic microwave background and the matter power spectrum at present. From a recent observational estimate of $\sigma_{8}$, we derive constraints on the lifetime of DDM and the mass ratio between the decay products and DDM. We also discuss implications of the DDM model for the discrepancy in the measurements of $\sigma_8$ recently claimed by the Planck satellite collaboration.

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S. Aoyama, T. Sekiguchi, K. Ichiki, et. al.
Fri, 14 Feb 14
2/42

Non-singular bounce scenarios in loop quantum cosmology and the effective field description [CL]

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http://arxiv.org/abs/1402.3009


A non-singular bouncing cosmology is generically obtained in loop quantum cosmology due to non-perturbative quantum gravity effects. A similar picture can be achieved in standard general relativity in the presence of a scalar field with a non-standard kinetic term such that at high energy densities the field evolves into a ghost condensate and causes a non-singular bounce. During the bouncing phase, the perturbations can be stabilized by introducing a Horndeski operator. Taking the matter content to be a dust field and an ekpyrotic scalar field, we compare the dynamics in loop quantum cosmology and in a non-singular bouncing effective field model with a non-standard kinetic term at both the background and perturbative levels. We find that these two settings share many important properties, including the result that they both generate scale-invariant scalar perturbations. This shows that some quantum gravity effects of the very early universe may be mimicked by effective field models.

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Y. Cai and E. Wilson-Ewing
Fri, 14 Feb 14
3/42

Star clusters in M33: updated UBVRI photometry, ages, metallicities, and masses [GA]

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http://arxiv.org/abs/1402.3029


The photometric characterization of M33 star clusters is far from complete. In this paper, we present homogeneous $UBVRI$ photometry of 708 star clusters and cluster candidates in M33 based on archival images from the Local Group Galaxies Survey, which covers 0.8 deg$^2$ along the galaxy’s major axis. Our photometry includes 387, 563, 616, 580, and 478 objects in the $UBVRI$ bands, respectively, of which 276, 405, 430, 457, and 363 do not have previously published $UBVRI$ photometry. Our photometry is consistent with previous measurements (where available) in all filters. We adopted Sloan Digital Sky Survey $ugriz$ photometry for complementary purposes, as well as Two Micron All-Sky Survey near-infrared $JHK$ photometry where available. We fitted the spectral-energy distributions of 671 star clusters and candidates to derive their ages, metallicities, and masses based on the updated {\sc parsec} simple stellar populations synthesis models. The results of our $\chi^2$ minimization routines show that only 205 of the 671 clusters ($31\%$) are older than 2 Gyr, which represents a much smaller fraction of the cluster population than that in M31 ($56\%$), suggesting that M33 is dominated by young star clusters ($<1$ Gyr). We investigate the mass distributions of the star clusters—both open and globular clusters—in M33, M31, the Milky Way, and the Large Magellanic Cloud. Their mean values are $\log(M_{\rm cl}/M_{\odot})=4.25$, 5.43, 2.72, and 4.18, respectively. The fraction of open to globular clusters is highest in the Milky Way and lowest in M31. Our comparisons of the cluster ages, masses, and metallicities show that our results are basically in agreement with previous studies (where objects in common are available); differences can be traced back to differences in the models adopted, the fitting methods used, and stochastic sampling effects.

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Z. Fan and R. Grijs
Fri, 14 Feb 14
6/42

Variability in Low Ionization Broad Absorption Line Outflows [CEA]

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http://arxiv.org/abs/1402.2980


We present results of our time variability studies of Mg II and Al III absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2 <= zem <= 2.1 using the 2m telescope at IUCAA Girawali Observatory over a time-scale of 10 days to 7.69 years in the QSO’s rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e >= 1 year) absorption line variability is seen in 8 cases (36% systems) while only 4 of them (i.e 18% systems) show variability over short time-scales (i.e < 1 year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in 2 cases and clear indications for profile variations in 4 cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight.

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M. Vivek, R. Srianand, P. Petitjean, et. al.
Fri, 14 Feb 14
7/42

Quantum tunneling of oxygen atoms on very cold surfaces [CL]

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http://arxiv.org/abs/1402.3207


Any evolving system can change of state via thermal mechanisms (hopping a barrier) or via quantum tunneling. Most of the time, efficient classical mechanisms dominate at high temperatures. This is why an increase of the temperature can initiate the chemistry. We present here an experimental investigation of O-atom diffusion and reactivity on water ice. We explore the 6-25 K temperature range at sub-monolayer surface coverages. We derive the diffusion temperature law and observe the transition from quantum to classical diffusion. Despite of the high mass of O, quantum tunneling is efficient even at 6 K. As a consequence, the solid-state astrochemistry of cold regions should be reconsidered and should include the possibility of forming larger organic molecules than previously expected.

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M. Minissale, E. Congiu, S. Baouche, et. al.
Fri, 14 Feb 14
8/42