Tag Archives: Cosmology and Extragalactic Astrophysics

Nonabelian Dark Matter with Resonant Annihilation [CL]

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http://arxiv.org/abs/1306.0882


We construct a model based on an extra gauge symmetry, SU(2)_X x U(1)_{B-L}, which can provide gauge bosons to serve as weakly-interacting massive particle dark matter. The stability of the dark matter is naturally guaranteed by a discrete Z_2 symmetry that is a subgroup of SU(2)_X. The dark matter interacts with standard model fermions by exchanging gauge bosons which are linear combinations of SU(2)_X x U(1)_{B-L} gauge bosons. With the appropriate choice of representation for the new scalar multiplet whose vacuum expectation value spontaneously breaks the SU(2)_X symmetry, the relation between the new gauge boson masses can naturally lead to resonant pair annihilation of the dark matter. After exploring the parameter space of the new gauge couplings subject to constraints from collider data and the observed relic density, we use the results to evaluate the cross section of the dark matter scattering off nucleons and compare it with data from the latest direct detection experiments. We find allowed parameter regions that can be probed by future direct searches for dark matter and LHC searches for new particles.

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C. Chiang, T. Nomura and J. Tandean
Fri, 7 Mar 14
27/47

Evolution of the Fraction of Clumpy Galaxies at 0.2<z<1.0 in the COSMOS field [CEA]

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http://arxiv.org/abs/1403.1496


Using the Hubble Space Telescope/Advanced Camera for Surveys data in the COSMOS field, we systematically searched clumpy galaxies at 0.2<z<1.0 and investigated the fraction of clumpy galaxies and its evolution as a function of stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction of clumpy galaxies in star-forming galaxies with Mstar > 10^9.5 Msun decreases with time from ~0.35 at 0.8<z<1.0 to ~0.05 at 0.2<z<0.4 irrespective of the stellar mass, although the fraction tends to be slightly lower for massive galaxies with Mstar > 10^10.5 Msun at each redshift. On the other hand, the fraction of clumpy galaxies increases with increasing both SFR and SSFR in all the redshift ranges we investigated. In particular, we found that the SSFR dependences of the fractions are similar among galaxies with different stellar masses, and the fraction at a given SSFR does not depend on the stellar mass in each redshift bin. The evolution of the fraction of clumpy galaxies from z~0.9 to z~0.3 seems to be explained by such SSFR dependence of the fraction and the evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also appears to decrease with time, but this can be due to the effect of the morphological K-correction. We suggest that these results are understood by the gravitational fragmentation model for the formation of giant clumps in disk galaxies, where the gas mass fraction is a crucial parameter.

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K. Murata, M. Kajisawa, Y. Taniguchi, et. al.
Fri, 7 Mar 14
29/47

A Model for Multi-property Galaxy Cluster Statistics [CEA]

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http://arxiv.org/abs/1403.1456


The massive dark matter halos that host groups and clusters of galaxies have observable properties that appear to be log-normally distributed about power-law mean scaling relations in halo mass. Coupling this assumption with either quadratic or cubic approximations to the mass function in log space, we derive closed-form expressions for the space density of halos as a function of multiple observables as well as forms for the low-order moments of properties of observable-selected samples. Using a Tinker mass function in a {\Lambda}CDM cosmology, we show that the cubic analytic model reproduces results obtained from direct, numerical convolution at the 10 percent level or better over nearly the full range of observables covered by current observations and for redshifts extending to z = 1.5. The model provides an efficient framework for estimating effects arising from selection and covariance among observable properties in survey samples.

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A. Evrard, P. Arnault, D. Huterer, et. al.
Fri, 7 Mar 14
30/47

SCoPE: An efficient method of Cosmological Parameter Estimation [CEA]

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http://arxiv.org/abs/1403.1271


Markov Chain Monte Carlo (MCMC) sampler is widely used for cosmological parameter estimation from CMB and other data. However, due to the intrinsic serial nature of the MCMC sampler, convergence is often very slow. Here we present a fast and independently written Monte Carlo method for cosmological parameter estimation named as Slick Cosmological Parameter Estimator (SCoPE), that employs delayed rejection to increase the acceptance rate of a chain, and pre-fetching that helps an individual chain to run on parallel CPUs. An inter-chain covariance update is also incorporated to prevent clustering of the chains allowing faster and better mixing of the chains. We use an adaptive method for covariance calculation to calculate and update the covariance automatically as the chains progress. Our analysis shows that the acceptance probability of each step in SCoPE is more than $95\%$ and the convergence of the chains are faster. Using SCoPE, we carry out some cosmological parameter estimations with different cosmological models using WMAP-9 and Planck results. One of the current research interests in cosmology is quantifying the nature of dark energy. We analyze the cosmological parameters from two illustrative commonly used parameterisations of dark energy models. We also asses primordial helium fraction in the universe can be constrained by the present CMB data from WMAP-9 and Planck. The results from our MCMC analysis on the one hand helps us to understand the workability of the SCoPE better, on the other hand it provides a completely independent estimation of cosmological parameters from WMAP-9 and Planck data.

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S. Das and T. Souradeep
Fri, 7 Mar 14
32/47

Cosmographic bounds on the cosmological deceleration-acceleration transition redshift in $f(\mathcal{R})$ gravity [CL]

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http://arxiv.org/abs/1403.1421


We examine the observational viability of a class of $f(\mathcal{R})$ gravity cosmological models. Particular attention is devoted to constraints from the recent observational determination of the redshift of the cosmological deceleration-acceleration transition. Making use of the fact that the Ricci scalar is a function of redshift $z$ in these models, $\mathcal {R=R}(z)$, and so is $f(z)$, we use cosmography to relate a $f(z)$ test function evaluated at higher $z$ to late-time cosmographic bounds. First, we consider a model independent procedure to build up a numerical $f(z)$ by requiring that at $z=0$ the corresponding cosmological model reduces to standard $\Lambda$CDM. We then infer late-time observational constraints on $f(z)$ in terms of bounds on the Taylor expansion cosmographic coefficients. In doing so we parameterize possible departures from the standard $\Lambda$CDM model in terms of a two-parameter logarithmic correction. The physical meaning of the two parameters is also discussed in terms of the post Newtonian approximation. Second, we provide numerical estimates of the cosmographic series terms by using Type Ia supernova apparent magnitude data and Hubble parameter measurements. Finally, we use these estimates to bound the two parameters of the logarithmic correction. We find that the deceleration parameter in our model changes sign at a redshift consistent with what is observed.

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S. Capozziello, O. Farooq, O. Luongo, et. al.
Fri, 7 Mar 14
35/47

Counter-Rotation in Disk Galaxies [GA]

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http://arxiv.org/abs/1403.1263


Counter-rotating galaxies host two components rotating in opposite directions with respect to each other. The kinematic and morphological properties of lenticulars and spirals hosting counter-rotating components are reviewed. Statistics of the counter-rotating galaxies and analysis of their stellar populations provide constraints on the formation scenarios which include both environmental and internal processes.

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E. Corsini
Fri, 7 Mar 14
37/47

Measuring the growth of matter fluctuations with third-order galaxy correlations [CEA]

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http://arxiv.org/abs/1403.1259


Measurements of the linear growth factor $D$ at different redshifts $z$ are key to distinguish among cosmological models. One can estimate the derivative $dD(z)/d\ln(1+z)$ from redshift space measurements of the 3D anisotropic galaxy two-point correlation $\xi(z)$, but the degeneracy of its transverse (or projected) component with galaxy bias, i.e. $\xi_{\perp}(z) \propto\ D^2(z) b^2(z)$, introduces large errors in the growth measurement. In this paper we present a detailed comparison of two methods that have been proposed in the literature to break this degeneracy. Both propose measuring $b(z)$, and therefore $D(z)$ via $\xi_{\perp}$, by combining second- and third-order statistics. One uses the shape of the reduced three-point correlation and the other a combination of third-order one- and two-point cumulants. These methods take advantage of the fact that, for Gaussian initial conditions, the reduced third-order matter correlations are independent of redshift (and therefore of the growth factor) while the corresponding galaxy correlations depend on $b$. One can therefore measure $b$ and $D$ by comparing the second- and third-order matter correlations to those of galaxies. We use matter and halo catalogs from the MICE-GC simulation to test how well we can recover $b(z)$ and $D(z)$ with these methods in 3D real space. We also present a new approach, which enables us to measure $D$ directly from the redshift evolution of second- and third-order galaxy correlations without the need of modelling matter correlations. For haloes with masses lower than $10^{14}$ $h^{-1}$M$_\odot$, we find a $10$ percent agreement between the different estimates of $D$. At higher masses we find larger differences that can probably be attributed to the breakdown of the local quadratic bias model and non-Poissonian shot-noise.

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K. Hoffmann, J. Bel, E. Gaztanaga, et. al.
Fri, 7 Mar 14
46/47

Reionization and CMB non-Gaussianity [CEA]

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http://arxiv.org/abs/1403.1531


We show how cross-correlating a high redshift {\em external} tracer field, such as the 21cm neutral hydrogen distribution and product maps involving Cosmic Microwave Background (CMB) temperature and polarisation fields, that probe mixed bispectrum involving these fields, can help to determine the reionization history of the Universe, beyond what can be achieved from cross-spectrum analysis. Taking clues from recent studies for the detection of primordial non-Gaussianity \citep{MuHe10}, we develop a set of estimators that can study reionization using a power spectrum associated with the bispectrum (or skew-spectrum). We use the matched filtering inherent in this method to investigate different reionization histories. We check to what extent they can be used to rule out various models of reionization and study cross contamination from different sources such as the lensing of the CMB. The estimators can be fine-tuned to optimize study of a specific reionization history. We consider three different types of tracers in our study, namely: proto-galaxies; 21cm maps of neutral hydrogen; quasars. We also consider four alternative models of reionization. We find that the signal-to-noise (S/N) for detection can reach $\mathcal{O}(70)$ for Planck-type experiments. The S/N depends on the specific choice of a tracer field, and multiple tracers can be effectively used to map out the entire reionization history with reasonable S/N. Contamination from weak lensing is investigated and found to be negligible, and the effects of Thomson scattering from patchy reionization are also considered.

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D. Munshi, P. Corasaniti, P. Coles, et. al.
Fri, 7 Mar 14
47/47

Cosmological constant in SUGRA models with Planck scale SUSY breaking and degenerate vacua [CL]

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http://arxiv.org/abs/1403.1001


We argue that the measured value of the cosmological constant, as well as the small values of quartic Higgs self–coupling and the corresponding beta function at the Planck scale, which can be obtained by extrapolating the Standard Model (SM) couplings to high energies, can originate from supergravity (SUGRA) models with degenerate vacua. This scenario is realised if there are at least three exactly degenerate vacua. In the first vacuum, associated with the physical one, local supersymmetry (SUSY) is broken near the Planck scale while the breakdown of the SU(2)_W\times U(1)_Y symmetry takes place at the electroweak (EW) scale. In the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than \Lambda_{QCD} in the physical vacuum. Finally, in the third vacuum local SUSY and EW symmetry are broken near the Planck scale.

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C. Froggatt, R. Nevzorov, H. Nielsen, et. al.
Thu, 6 Mar 14
3/53

Cosmological observables in multi-field inflation with a non-flat field space [CL]

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http://arxiv.org/abs/1403.0654


Using $\delta N$ formalism, in the context of a generic multi-field inflation driven on a non-flat field space background, we revisit the analytic expressions of the various cosmological observables such as scalar/tensor power spectra, scalar/tensor spectral tilts, non-Gaussianity parameters, tensor-to-scalar ratio, and the various runnings of these observables. Utilizing the subsequent analytic expressions for various cosmological observables, in the light of PLANCK results, we examine for the compatibility of the consistency relations within the slow-roll regime of a two-field roulette poly-instanton inflation realized in the context of large volume scenarios.

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X. Gao, T. Li and P. Shukla
Thu, 6 Mar 14
4/53

Self-interacting asymmetric dark matter coupled to a light massive dark photon [CL]

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http://arxiv.org/abs/1403.1077


Dark matter (DM) with sizeable self-interactions mediated by a light species offers a compelling explanation of the observed galactic substructure; furthermore, the direct coupling between DM and a light particle contributes to the DM annihilation in the early universe. If the DM abundance is due to a dark particle-antiparticle asymmetry, the DM annihilation cross-section can be arbitrarily large, and the coupling of DM to the light species can be significant. We consider the case of asymmetric DM interacting via a light (but not necessarily massless) Abelian gauge vector boson, a dark photon. In the massless dark photon limit, gauge invariance mandates that DM be multicomponent, consisting of positive and negative dark ions of different species which partially bind in neutral dark atoms. We argue that a similar conclusion holds for light dark photons; in particular, we establish that the multi-component and atomic character of DM persists in much of the parameter space where the dark photon is sufficiently light to mediate sizeable DM self-interactions. We discuss the cosmological sequence of events in this scenario, including the dark asymmetry generation, the freeze-out of annihilations, the dark recombination and the phase transition which gives mass to the dark photon. We estimate the effect of self-interactions in DM haloes, taking into account this cosmological history. We place constraints based on the observed ellipticity of large haloes, and identify the regimes where DM self-scattering can affect the dynamics of smaller haloes, bringing theory in better agreement with observations. Moreover, we estimate the cosmological abundance of dark photons in various regimes, and derive pertinent bounds. We discuss the interplay between these bounds, the DM self-interaction in haloes and the requirement for efficient DM annihilation in the early universe.

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K. Petraki, L. Pearce and A. Kusenko
Thu, 6 Mar 14
5/53

The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium [CEA]

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http://arxiv.org/abs/1403.0947


We analyze the physical conditions of the cool (T ~ 10^4 K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements taken along 38 quasar sightlines passing within 160 kpc of L ~ L* galaxies at z~0.2. These data are well described by simple photoionization models, with the gas highly ionized (n_HII/n_H > 99%) by the extragalactic ultraviolet background (EUVB). Scaling by estimates for the virial radius, R_vir, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. This correlation has a power-law form of U = (0.006 +/- 0.003)(R/R_vir)^(0.8 +/- 0.3), with significant scatter. The ionization parameters imply a decreasing volume density profile n_ H = 10^(-4.2 +/- 0.25) (R/R_vir)^(-0.8 +/-0.3). Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, diffuse medium. Applying the ionization corrections to the HI column densities, we estimate a lower limit to the cool gas mass M_ CGMcool > 6.5 x 10^10 M_sun for the volume within R < R_vir. Allowing for an additional warm, OVI-traced phase, the CGM accounts for *at least* half of the baryons purported to be missing from galaxy dark matter halos.

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J. Werk, J. Prochaska, J. Tumlinson, et. al.
Thu, 6 Mar 14
6/53

Broad Absorption Line Variability in Radio-Loud Quasars [CEA]

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http://arxiv.org/abs/1403.0958


We investigate C IV broad absorption line (BAL) variability within a sample of 46 radio-loud quasars (RLQs), selected from SDSS/FIRST data to include both core-dominated (39) and lobe-dominated (7) objects. The sample consists primarily of high-ionization BAL quasars, and a substantial fraction have large BAL velocities or equivalent widths; their radio luminosities and radio-loudness values span ~2.5 orders of magnitude. We have obtained 34 new Hobby-Eberly Telescope (HET) spectra of 28 BAL RLQs to compare to earlier SDSS data, and we also incorporate archival coverage (primarily dual-epoch SDSS) for a total set of 78 pairs of equivalent width measurements for 46 BAL RLQs, probing rest-frame timescales of ~80-6000 d (median 500 d). In general, only modest changes in the depths of segments of absorption troughs are observed, akin to those seen in prior studies of BAL RQQs. Also similar to previous findings for RQQs, the RLQs studied here are more likely to display BAL variability on longer rest-frame timescales. However, typical values of |Delta_EW| and |Delta_EW|/<EW> are about 40+/-20% lower for BAL RLQs when compared with those of a timescale-matched sample of BAL RQQs. Optical continuum variability is of similar amplitude in BAL RLQs and BAL RQQs; for both RLQs and RQQs, continuum variability tends to be stronger on longer timescales. BAL variability in RLQs does not obviously depend upon their radio luminosities or radio-loudness values, but we do find tentative evidence for greater fractional BAL variability within lobe-dominated RLQs. Enhanced BAL variability within more edge-on (lobe-dominated) RLQs supports some geometrical dependence to the outflow structure.

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C. Welling, B. Miller, W. Brandt, et. al.
Thu, 6 Mar 14
8/53

Star formation rates in nearby Markarian galaxies [GA]

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http://arxiv.org/abs/1403.1066


The star formation rates for the 230 nearest Markarian galaxies with radial velocities V_LG<3500 km/s have been determined from their far ultraviolet fluxes obtained with the GALEX satellite. We briefly discuss the observed relationship between the star formation rate and other integral parameters of these galaxies: stellar mass, hydrogen mass, morphological type, and activity index. On the average, the Markarian galaxies have reserves of gas that are a factor of two smaller than those of galaxies in the field of the same stellar mass and type. Despite their elevated activity, the specific rate of star formation in the Markarian galaxies, SFR/M_*, does not exceed a limit of ~dex(-9.4) [yr^-1].

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V. Karachentseva, O. Melnyk and I. Karachentsev
Thu, 6 Mar 14
9/53

Type II-Plateau supernovae as metallicity probes of the Universe [SSA]

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http://arxiv.org/abs/1403.1167


We explore a method for metallicity determinations based on quantitative spectroscopy of type II-Plateau (II-P) supernovae (SNe). For consistency, we first evolve a set of 15Msun main sequence stars at 0.1, 0.4, 1, and 2 x the solar metallicity. At the onset of core collapse, we trigger a piston-driven explosion and model the resulting ejecta and radiation. Our theoretical models of such red-supergiant-star explosions at different metallicity show that synthetic spectra of SNe II-P possess optical signatures during the recombination phase that are sensitive to metallicity variations. This sensitivity can be quantified and the metallicity inferred from the strength of metal-line absorptions. Furthermore, these signatures are not limited to O, but also include Na, Ca, Sc, Ti, or Fe. When compared to a sample of SNe II-P from the Carnegie SN Project and previous SN followup programs, we find that most events lie at a metallicity between 0.4 and 2 x solar, with a marked scarcity of SN II-P events at SMC metallicity. This most likely reflects the paucity of low metallicity star forming regions in the local Universe.
SNe II-P have high plateau luminosities that make them observable spectroscopically at large distances. Because they exhibit signatures of diverse metal species, in the future they may offer a means to constrain the evolution of the composition (e.g., the O/Fe ratio) in the Universe out to a redshift of one and beyond.

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L. Dessart, C. Gutierrez, M. Hamuy, et. al.
Thu, 6 Mar 14
10/53

Satellite Alignment: I. Distribution of Substructures and Their Dependence On Assembly History From N-Body Simulations [CEA]

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http://arxiv.org/abs/1403.1008


Observations have shown that the spatial distribution of satellite galaxies is not random, but aligned with the major axes of central galaxies. This alignment is dependent on galaxy properties, such that red satellites are more strongly aligned than blue satellites. Theoretical work done to interpret this phenomena has found that it is due to the non-spherical nature of dark matter halos. However, most studies over-predict the alignment signal under the assumption that the central galaxy shape follows the shape of the host halo. It is also not clear whether the color dependence of alignment is due to an assembly bias or an evolution effect. In this paper we study these problems using a cosmological N-body simulation. Subhalos are used to trace the positions of satellite galaxies. It is found that the shape of dark matter halos are mis-aligned at different radii. If the central galaxy shares the same shape as the inner host halo, then the alignment effect is weaker and agrees with observational data. However, it predicts almost no dependence of alignment on the color of satellite galaxies, though the late accreted subhalos show stronger alignment with the outer layer of the host halo than their early accreted counterparts. We find that this is due to the limitation of pure N-body simulations that satellites galaxies without associated subhalos (‘orphan galaxies’) are not resolved. These orphan (mostly red) satellites often reside in the inner region of host halos and should follow the shape of the host halo in the inner region.

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Y. Wang, W. Lin, X. Kang, et. al.
Thu, 6 Mar 14
11/53

Metal-line absorption around $z\approx$2.4 star-forming galaxies in the Keck Baryonic Structure Survey [CEA]

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http://arxiv.org/abs/1403.0942


(Abridged) We study metal absorption by the circumgalactic medium of 843 $z\approx$2.4 star-forming galaxies taken from the Keck Baryonic Structure Survey. The galaxies examined in this work lie in the fields of 15 background QSOs, which all have high-quality Keck/HIRES spectra, with galaxy impact parameters ranging from 35 kpc to 2 Mpc. Using the pixel optical depth technique, we present the first galaxy-centred 2-D maps of the median absorption by OVI, NV, CIV, CIII, and SIV, as well as updated results for HI. At small galactocentric radii the absorption is strongly enhanced. The enhancement extends out to at least 180 kpc for OVI, CIII and SiIV (and 2 Mpc for HI and CIV) in the transverse direction, and $\pm$240 km/s along the line of sight (which would correspond to ~1 Mpc in the case of pure Hubble flow). After normalising the median absorption profiles to account for variations in line strengths and detection limits, we find no evidence for differences in the spatial distribution between HI and metals. We also present measurements of the scatter in the optical depths, covering factors, and equivalent widths as a function of projected galaxy distance. The current sample contains 318 galaxies whose redshifts have been measured from nebular emission lines using MOSFIRE, and have uncertainties of only ~18 km/s, compared to ~150 km/s for the previous determinations using rest-frame UV spectra. Limiting the sample to galaxies with nebular emission line redshifts does not decrease the extent of the enhancement along the line of sight compared to that in the transverse direction. This rules out redshift errors as the source of the observed redshift-space anisotropy and thus implies that we have detected the signature of gas peculiar velocities from infall, outflows, or virial motions for HI, OVI, CIV, CIII, and SiIV.

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M. Turner, J. Schaye, C. Steidel, et. al.
Thu, 6 Mar 14
12/53

Lifshitz spacetimes, solitons, and generalized BTZ black holes in quantum gravity at a Lifshitz point [CL]

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http://arxiv.org/abs/1403.0946


In this paper, we study static vacuum solutions of quantum gravity at a fixed Lifshitz point in (2+1) dimensions, and present all the diagonal solutions in closed forms in the infrared limit. The exact solutions represent spacetimes with very rich structures: they can represent generalized BTZ black holes, Lifshitz space-times or Lifshitz solitons, in which the spacetimes are free of any kind of space-time singularities, depending on the choices of the free parameters of the solutions. We also find several classes of exact static non-diagonal solutions, which represent similar space-time structures as those given in the diagonal case. The relevance of these solutions to the non-relativistic Lifshitz-type gauge/gravity duality is discussed.

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F. Shu, K. Lin, A. Wang, et. al.
Thu, 6 Mar 14
14/53

A PCA-based automated finder for galaxy-scale strong lenses [IMA]

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http://arxiv.org/abs/1403.1063


We present an algorithm using Principal Component Analysis (PCA) to subtract galaxies from imaging data, and also two algorithms to find strong, galaxy-scale gravitational lenses in the resulting residual image. The combined method is optimized to find full or partial Einstein rings. Starting from a pre-selection of potential massive galaxies, we first perform a PCA to build a set of basis vectors. The galaxy images are reconstructed using the PCA basis and subtracted from the data. We then filter the residual image with two different methods. The first uses a curvelet (curved wavelets) filter of the residual images to enhance any curved/ring feature. The resulting image is transformed in polar coordinates, centered on the lens galaxy center. In these coordinates, a ring is turned into a line, allowing us to detect very faint rings by taking advantage of the integrated signal-to-noise in the ring (a line in polar coordinates). The second way of analysing the PCA-subtracted images identifies structures in the residual images and assesses whether they are lensed images according to their orientation, multiplicity and elongation. We apply the two methods to a sample of simulated Einstein rings, as they would be observed with the ESA Euclid satellite in the VIS band. The polar coordinates transform allows us to reach a completeness of 90% and a purity of 86%, as soon as the signal-to-noise integrated in the ring is higher than 30, and almost independent of the size of the Einstein ring. Finally, we show with real data that our PCA-based galaxy subtraction scheme performs better than traditional subtraction based on model fitting to the data. Our algorithm can be developed and improved further using machine learning and dictionary learning methods, which would extend the capabilities of the method to more complex and diverse galaxy shapes.

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R. Joseph, F. Courbin, R. Metcalf, et. al.
Thu, 6 Mar 14
17/53

Use of spatial cross correlation function to study formation mechanism of massive elliptical galaxies [CL]

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http://arxiv.org/abs/1403.1057


Spatial clustering nature of galaxies have been studied previously through auto correlation function. The same type of cross correlation function has been used to investigate parametric clustering nature of galaxies e.g. with respect to masses and sizes of galaxies.
Here formation and evolution of several components of nearby massive early type galaxies have been envisaged through cross correlations, in the mass-size parametric plane, with high redshift early type galaxies (hereafter ETG).It is found that the inner most components of nearby ETGs have significant correlation with ETGs in the highest redshift range called red nuggets whereas intermediate components are highly correlated with ETGs in the redshift range with z value greater than 0.5 and less than 0.75. The outer most part has no correlation in any range, suggesting a scenario through in situ accretion. The above formation scenario is consistent with the previous results obtained for NGC5128 (Chattopadhyay et al. (2009), Chattopadhyay et al. (2013)) and to some extent for nearby elliptical galaxies (Huang et al. (2013)) after considering a sample of ETGs at high redshift with stellar masses greater than or equal to 108.73 M-Sun. So the present work indicates a three phase formation of massive nearby elliptical galaxies instead of two as discussed in previous works.

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T. De, T. Chattopadhyay and A. Chattopadhyay
Thu, 6 Mar 14
20/53

Cosmology with Ricci-type dark energy [CEA]

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http://arxiv.org/abs/1403.1103


We consider the dynamics of a cosmological substratum of pressureless matter and holographic dark energy with a cutoff length proportional to the Ricci scale. Stability requirements for the matter perturbations are shown to single out a model with a fixed relation between the present matter fraction $\Omega_{m0}$ and the present value $\omega_{0}$ of the equation-of-state parameter of the dark energy. This model has the same number of free parameters as the $\Lambda$CDM model but it has no $\Lambda$CDM limit. We discuss the consistency between background observations and the mentioned stability-guaranteeing parameter combination.

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W. Zimdahl, J. Fabris, S. Campo, et. al.
Thu, 6 Mar 14
22/53

Primordial Magnetic Helicity from Stochastic Electric Currents [CEA]

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http://arxiv.org/abs/1403.1193


We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, $H_M$. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point SQED Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle non null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of $H_M$ for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is $D = 1/2$. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case the fractal dimension is $D=0$. We finally estimate the intensity of fields induced at the horizon scale of reheating, and evolve them until the decoupling of matter and radiation under the hypothesis of inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation.

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E. Calzetta and A. Kandus
Thu, 6 Mar 14
25/53

The nature of supernovae 2010O and 2010P in Arp 299 – II. Radio emission [GA]

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http://arxiv.org/abs/1403.1036


We report radio observations of two stripped-envelope supernovae (SNe), 2010O and 2010P, which exploded within a few days of each other in the luminous infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio frequencies, SN 2010P was detected (with an astrometric accuracy better than 1 milli arcsec in position) in its optically thin phase in epochs ranging from ~1 to ~3yr after its explosion date, indicating a very slow radio evolution and a strong interaction of the SN ejecta with the circumstellar medium. Our late-time radio observations toward SN 2010P probe the dense circumstellar envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of ~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type IIb classification for SN 2010P, making it the most distant and most slowly evolving Type IIb radio SN detected to date.

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C. Romero-Canizales, R. Herrero-Illana, M. Perez-Torres, et. al.
Thu, 6 Mar 14
26/53

Two-dimensional Lorentz invariance of spherically symmetric black holes [CL]

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http://arxiv.org/abs/1402.6707


We show that a static spherically symmetric black hole, in a generic theory of gravity with generic matter fields, has a two-dimensional Lorentz symmetry.

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L. Hui and A. Nicolis
Thu, 6 Mar 14
29/53

RingFinder: automated detection of galaxy-scale gravitational lenses in ground-based multi-filter imaging data [CEA]

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http://arxiv.org/abs/1403.1041


We present RingFinder, a tool for finding galaxy-scale strong gravitational lenses in multiband imaging data. By construction, the method is sensitive to configurations involving a massive foreground early-type galaxy and a faint, background, blue source. RingFinder detects the presence of blue residuals embedded in an otherwise smooth red light distribution by difference imaging in two bands. The method is automated for efficient application to current and future surveys, having originally been designed for the 150-deg2 Canada France Hawaii Telescope Legacy Survey (CFHTLS). We describe each of the steps of RingFinder. We then carry out extensive simulations to assess completeness and purity. For sources with magnification mu>4, RingFinder reaches 42% (resp. 25%) completeness and 29% (resp. 86%) purity before (resp. after) visual inspection. The completeness of RingFinder is substantially improved in the particular range of Einstein radii 0.8 < REin < 2. and lensed images brighter than g = 22.5, where it can be as high as 70%. RingFinder does not introduce any significant bias in the source or deflector population. We conclude by presenting the final catalog of RingFinder CFHTLS galaxy-scale strong lens candidates. Additional information obtained with Hubble Space Telescope and Keck Adaptive Optics high resolution imaging, and with Keck and Very Large Telescope spectroscopy, is used to assess the validity of our classification, and measure the redshift of the foreground and the background objects. From an initial sample of 640,000 early type galaxies, RingFinder returns 2500 candidates, which we further reduce by visual inspection to 330 candidates. We confirm 33 new gravitational lenses from the main sample of candidates, plus an additional 16 systems taken from earlier versions of RingFinder. First applications are presented in the SL2S galaxy-scale Lens Sample paper series.

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R. Gavazzi, P. Marshall, T. Treu, et. al.
Thu, 6 Mar 14
30/53

On the use of semi-numerical simulations in predicting the 21-cm signal from the epoch of reionization [CEA]

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http://arxiv.org/abs/1403.0941


We perform a detailed comparison of three different simulations of the neutral hydrogen distribution during the epoch of reionization (EoR). Our benchmark is a radiative transfer simulation (C2RAY). Such simulations can produce realistic results, but are computationally expensive. We compare it with two different semi-numerical techniques: one using the same halos as C2RAY as its sources (Sem-Num), and one using a conditional Press-Schechter scheme (CPS+GS). These are more computationally efficient than C2RAY, but use more simplistic physics. We evaluate them in terms of how well they can reproduce the history and morphology of EoR. We find that Sem-Num can produce an ionization history and morphology that is very close to C2RAY. Considering the effects of redshift space distortions due to peculiar velocities, we also study a number of statistics such as: the variance, spherically averaged power spectrum and various angular multipole moments of the power spectrum of the 21-cm signal from EoR,that will be observable by upcoming radio telescopes. We find that both semi-numerical models perform quite well in predicting these observables at length scales relevant for the present and future experiments. We also observe that predictions from Sem-Num are slightly better (by $\sim 10\%$) than CPS+GS for most of the observables. However, the predictions for the reionization history and the morphology of the ionization maps are significantly better (by $\sim 25-50\%$) in Sem-Num than CPS+GS. As the predictions for the 21-cm signal together with the reionization history would be required for parametrization of EoR from the observations, it would be better to use a semi-numerical simulation which can predict both with an acceptable accuracy. Our analysis shows that among the two semi-numerical simulations Sem-Num satisfies this criteria very well as it uses a source model very similar to C2RAY.

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S. Majumdar, G. Mellema, K. Datta, et. al.
Thu, 6 Mar 14
32/53

A Critical Look at the Standard Cosmological Picture [CL]

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http://arxiv.org/abs/1303.2549


The discovery that the Universe is accelerating in its expansion has brought the basic concept of cosmic expansion into question. An analysis of the evolution of this concept suggests that the paradigm that was finally settled into prior to that discovery was not the best option, as the observed acceleration lends empirical support to an alternative which could incidentally explain expansion in general. I suggest, then, that incomplete reasoning regarding the nature of cosmic time in the derivation of the standard model is the reason why the theory cannot coincide with this alternative concept. Therefore, through an investigation of the theoretical and empirical facts surrounding the nature of cosmic time, I argue that an enduring three-dimensional cosmic present must necessarily be assumed in relativistic cosmology—and in a stricter sense than it has been. Finally, I point to a related result which could offer a better explanation of the empirically constrained expansion rate.

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D. Janzen
Thu, 6 Mar 14
33/53

Material models of dark energy [CEA]

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http://arxiv.org/abs/1403.1213


We review and develop a new class of “dark energy” models, in which the relativistic theory of solids is used to construct material models of dark energy. These are models which include the effects of a continuous medium with well defined physical properties at the level of linearized perturbations. The formalism is constructed for a medium with arbitrary symmetry, and then specialised to isotropic media (which will be the case of interest for the majority of cosmological applications). We develop the theory of relativistic isotropic viscoelastic media whilst keeping in mind that we ultimately want to observationally constrain the allowed properties of the material model. We do this by obtaining the viscoelastic equations of state for perturbations (the entropy and anisotropic stress), as well as identifying the consistent corner of the theory which has constant equation of state parameter $\dot{w}=0$. We also connect to the non-relativistic theory of solids, by identifying the two quadratic invariants that are needed to construct the energy-momentum tensor, namely the Rayleigh dissipation function and Lagrangian for perturbations. Finally, we develop the notion that the viscoelastic behavior of the medium can be thought of as a non-minimally coupled massive gravity theory. This also provides a tool-kit for constructing consistent generalizations of coupled dark energy theories.

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J. Pearson
Thu, 6 Mar 14
37/53

Decaying Dark Atom constituents and cosmic positron excess [CEA]

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http://arxiv.org/abs/1403.1212


We present a scenario where dark matter is in the form of dark atoms that can accomodate the experimentally observed excess of positrons in PAMELA and AMS-02 while being compatible with the constraints imposed on the gamma-ray flux from Fermi/LAT. This scenario assumes that the dominant component of dark matter is in the form of a bound state between a helium nucleus and a $-2$ particle and a small component is in the form of a WIMP-like dark atom compatible with direct searches in underground detectors. One of the constituents of this WIMP-like state is a $+2$ metastable particle with a mass of 1 TeV or slightly below that by decaying to $e^+e^+$, $\mu^+ \mu^+$ and $\tau^+ \tau^+$ produces the observed positron excess. These decays can naturally take place via GUT interactions. If it exists, such a metastable particle can be found in the next run of LHC. The model predicts also the ratio of leptons over baryons in the Universe to be close to -3.

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K. Belotsky, M. Khlopov, C. Kouvaris, et. al.
Thu, 6 Mar 14
40/53

Resonantly-Produced 7 keV Sterile Neutrino Dark Matter Models and the Properties of Milky Way Satellites [CEA]

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http://arxiv.org/abs/1403.0954


Sterile neutrinos produced through a resonant Shi-Fuller mechanism are arguably the simplest model for a dark matter interpretation origin of the recent unidentified X-ray line seen toward a number of objects harboring dark matter. Here, I calculate the exact parameters required in this mechanism to produce the signal. The suppression of small scale structure predicted by these models is consistent with Local Group and high-$z$ galaxy count constraints. Very significantly, the parameters necessary in these models to produce the full dark matter density fulfill previously determined requirements to successfully match the Milky Way Galaxy’s total satellite abundance, the satellites’ radial distribution and their mass density profile, or “too big to fail problem.” I also discuss how further precision determinations of the detailed properties of the candidate sterile neutrino dark matter can probe the nature of the quark-hadron transition, which takes place during the dark matter production.

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K. Abazajian
Thu, 6 Mar 14
41/53

Spatial and Kinematic Distributions of Transition Populations in Intermediate Redshift Galaxy Clusters [CEA]

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http://arxiv.org/abs/1403.1115


We analyze the spatial and velocity distributions of confirmed members in five massive clusters of galaxies at intermediate redshift (0.5 < z < 0.9) to investigate the physical processes driving galaxy evolution. Based on spectral classifications derived from broad- and narrow-band photometry, we define four distinct galaxy populations representing different evolutionary stages: red sequence (RS) galaxies, blue cloud (BC) galaxies, green valley (GV) galaxies, and luminous compact blue galaxies (LCBGs). For each galaxy class, we derive the projected spatial and velocity distribution and characterize the degree of subclustering. We find that RS, BC, and GV galaxies in these clusters have similar velocity distributions, but that BC and GV galaxies tend to avoid the core of the two z~0.55 clusters. GV galaxies exhibit subclustering properties similar to RS galaxies, but their radial velocity distribution is significantly platykurtic compared to the RS galaxies. The absence of GV galaxies in the cluster cores may explain their somewhat prolonged star-formation history. The LCBGs appear to have recently fallen into the cluster based on their larger velocity dispersion, absence from the cores of the clusters, and different radial velocity distribution than the RS galaxies. Both LCBG and BC galaxies show a high degree of subclustering on the smallest scales, leading us to conclude that star formation is likely triggered by galaxy-galaxy interactions during infall into the cluster.

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S. Crawford, G. Wirth and M. Bershady
Thu, 6 Mar 14
45/53

Primordial Black Holes: sirens of the early Universe [CL]

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http://arxiv.org/abs/1403.1198


Primordial Black Holes (PBHs) are, typically light, black holes which can form in the early Universe. There are a number of formation mechanisms, including the collapse of large density perturbations, cosmic string loops and bubble collisions. The number of PBHs formed is tightly constrained by the consequences of their evaporation and their lensing and dynamical effects. Therefore PBHs are a powerful probe of the physics of the early Universe, in particular models of inflation. They are also a potential cold dark matter candidate.

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A. Green
Thu, 6 Mar 14
47/53

Recursive structure in the definitions of gauge-invariant variables for any order perturbations [CL]

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http://arxiv.org/abs/1403.1004


The construction of gauge-invariant variables for any order perturbations is discussed. Explicit constructions of the gauge-invariant variables for perturbations to 4th order are shown. From these explicit construction, the recursive structure in the definitions of gauge-invariant variables for any order perturbations is found. Through this recursive structure, the correspondence with the fully non-linear exact perturbations is briefly discussed.

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K. Nakamura
Thu, 6 Mar 14
48/53

Transient spirals as superposed instabilities [GA]

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http://arxiv.org/abs/1403.1135


We present evidence that recurrent spiral activity, long manifested in simulations of disk galaxies, results from the super-position of a few transient spiral modes. Each mode lasts between five and ten rotations at its corotation radius where its amplitude is greatest. The scattering of stars as each wave decays takes place over narrow ranges of angular momentum, causing abrupt changes to the impedance of the disk to subsequent traveling waves. Partial reflections of waves at these newly created features, allows new standing-wave instabilities to appear that saturate and decay in their turn, scattering particles at new locations, creating a recurring cycle. The spiral activity causes the general level of random motion to rise, gradually decreasing the ability of the disk to support further activity unless the disk contains a dissipative gas component from which stars form on near-circular orbits. We also show that this interpretation is consistent with the behavior reported in other recent simulations with low mass-disks.

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J. Sellwood and R. Carlberg
Thu, 6 Mar 14
52/53

A comparison of CMB Angular Power Spectrum Estimators at Large Scales: the TT case [CEA]

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http://arxiv.org/abs/1403.1089


In the context of cosmic microwave background (CMB) data analysis, we compare the efficiency at large scale of two angular power spectrum algorithms, implementing, respectively, the quadratic maximum likelihood (QML) estimator and the pseudo spectrum (pseudo-Cl) estimator. By exploiting 1000 realistic Monte Carlo (MC) simulations, we find that the QML approach is markedly superior in the range l=[2-100]. At the largest angular scales, e.g. l < 10, the variance of the QML is almost 1/3 (1/2) that of the pseudo-Cl, when we consider the WMAP kq85 (kq85 enlarged by 8 degrees) mask, making the pseudo spectrum estimator a very poor option. Even at multipoles l=[20-60], where pseudo-Cl methods are traditionally used to feed the CMB likelihood algorithms, we find an efficiency loss of about 20%, when we considered the WMAP kq85 mask, and of about 15% for the kq85 mask enlarged by 8 degrees. This should be taken into account when claiming accurate results based on pseudo-Cl methods. Some examples concerning typical large scale estimators are provided.

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D. Molinari, A. Gruppuso, G. Polenta, et. al.
Thu, 6 Mar 14
53/53

Fossil Groups Origins IV. The relation between optical and X-ray luminosities [CEA]

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http://arxiv.org/abs/1403.0590


This study is part of the FOssil Groups Origin (FOGO) project which aims at carrying out a systematic and multiwavelength study of a large sample of fossil systems. Here we focus on the relation between the optical luminosity (Lopt) and X-ray luminosity (Lx). Out of a sample of 28 candidate fossil systems, we consider a sample of 12 systems whose fossil classification has been confirmed by a companion study. They are compared with the complementary sample of 16 systems whose fossil nature is not confirmed and with a subsample of 102 galaxy systems from the RASS-SDSS galaxy cluster survey. Fossil and normal systems span the same redshift range 0<z<0.5 and have the same Lx distribution. For each fossil system, the Lx in the 0.1-2.4 keV band is computed using data from the ROSAT All Sky Survey. For each fossil and normal system we homogeneously compute Lopt in the r-band within the characteristic cluster radius, using data from the SDSS DR7. We sample the Lx-Lopt relation over two orders of magnitude in Lx. Our analysis shows that fossil systems are not statistically distinguishable from the normal systems both through the 2D KS test and the fit of the Lx-Lopt relation. The optical luminosity of the galaxy system does strongly correlate with the X-ray luminosity of the hot gas component, independently of whether the system is fossil or not. We conclude that our results are consistent with the classical “merging scenario” of the brightest galaxy formed via merger/cannibalism of other group galaxies, with conservation of the optical light. We find no evidence for a peculiar state of the hot intracluster medium.

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M. Girardi, J. Aguerri, S. Grandi, et. al.
Wed, 5 Mar 14
1/75

The 7 keV axion dark matter and the X-ray line signal [CL]

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http://arxiv.org/abs/1402.6965


We propose a scenario where the saxion dominates the energy density of the Universe and reheats the standard model sector via the dilatonic coupling, while its axionic partner contributes to dark matter decaying into photons via the same operator in supersymmetry. Interestingly, for the axion mass $m_a \simeq 7$keV and the decay constant $f_a \simeq 10^{14-15}$GeV, the recently discovered X-ray line at $3.5$keV in the XMM Newton X-ray observatory data can be explained. We discuss various cosmological aspects of the $7$keV axion dark matter such as the production of axion dark matter, the saxion decay process, hot dark matter and isocurvature constraints on the axion dark matter, and the possible baryogenesis scenarios.

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T. Higaki, K. Jeong and F. Takahashi
Wed, 5 Mar 14
2/75

Constraints on the star-formation rate of z~3 LBGs with measured metallicity in the CANDELS GOODS-South field [CEA]

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http://arxiv.org/abs/1403.0743


We analyse 14 LBGs at z~2.8-3.8 constituting the only sample where both a spectroscopic measurement of their metallicity and deep IR observations (CANDELS+HUGS survey) are available. Fixing the metallicity of population synthesis models to the observed values, we determine best-fit physical parameters under different assumptions on the star-formation history and considering also the effect of nebular emission. For comparison we determine the UV slope of the objects, and use it to estimate their SFR_UV99 by correcting the UV luminosity following Meurer et al. (1999). A comparison between SFR obtained through SED-fitting (SFR_fit) and the SFR_UV99 shows that the latter are underestimated by a factor 2-10, regardless of the assumed SFH. Other SFR indicators (radio, far-IR, X-ray, recombination lines) coherently indicate SFRs a factor 2-4 larger than SFR_UV99 and in closer agreement with SFR_fit. Such discrepancy is due to the solar metallicity implied by the usual beta-A1600 conversion factor. We propose a refined relation, appropriate for sub-solar metallicity LBGs: A1600 = 5.32+1.99beta. This relation reconciles the dust-corrected UV with the SED-fitting and the other SFR indicators. We show that the fact that z~3 galaxies have sub-solar metallicity implies an upward revision by a factor of ~1.5-2 of the global SFRD, depending on the assumptions on the age of the stellar populations. We find very young best-fit ages (10-500 Myrs) for all our objects. From a careful examination of the uncertainties in the fit and the amplitude of the Balmer break we conclude that there is little evidence for the presence of old stellar population in at least half of the LBGs in our sample, suggesting that these objects are probably caught during a huge star-formation burst, rather than being the result of a smooth evolution.

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M. Castellano, V. Sommariva, A. Fontana, et. al.
Wed, 5 Mar 14
4/75

An analytic calculation of the growth index for $f(R)$ dark energy model [CEA]

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http://arxiv.org/abs/1403.0655


We derive the analytic formula of the growth index for $f(R)$ dark energy model where the effect on the growth of matter density perturbation $\delta_m$ from modified gravity (MG) is encoded in the effective Newton coupling constant $G_{\rm eff}$ in MG (or equivalently $g\equiv {G_{\rm eff}/ G}$). Based on the analytic formula, we propose that the parameter $g$ can be directly figured out by comparing the observed growth rate $f_g\equiv d\ln\delta_m/d\ln a$ to the prediction of $f_g$ in general relativity.

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Q. Huang
Wed, 5 Mar 14
5/75

On the effect of rotation on populations of classical Cepheids I. Predictions at solar metallicity [SSA]

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http://arxiv.org/abs/1403.0809


[Abridged] We aim to improve the understanding of Cepheids from an evolutionary perspective and establish the role of rotation in the Cepheid paradigm. In particular, we are interested in the contribution of rotation to the problem of Cepheid masses, and explore testable predictions of quantities that can be confronted with observations. Evolutionary models including a homogeneous and self-consistent treatment of rotation are studied in detail during the crossings of the classical instability strip (IS). The dependence of several parameters on initial rotation is studied. These parameters include mass, luminosity, temperature, lifetimes, equatorial velocity, surface abundances, and rates of period change. Several key results are obtained: i) mass-luminosity (M-L) relations depend on rotation, particularly during the blue loop phase; ii) luminosity increases between crossings of the IS. Hence, Cepheid M-L relations at fixed initial rotation rate depend on crossing number (faster rotation yields greater luminosity difference between crossings); iii) the Cepheid mass discrepancy problem vanishes when rotation and crossing number are taken into account, without a need for high core overshooting values or enhanced mass loss; iv) rotation creates dispersion around average parameters predicted at fixed mass and metallicity. This is of particular importance for the period-luminosity-relation, for which rotation is a source of intrinsic dispersion; v) enhanced surface abundances do not unambiguously distinguish Cepheids occupying the Hertzsprung gap from ones on blue loops (after dredge-up), since rotational mixing can lead to significantly enhanced Main Sequence (MS) abundances; vi) rotating models predict greater Cepheid ages than non-rotating models due to longer MS lifetimes. Rotation has a significant evolutionary impact on classical Cepheids and should no longer be neglected in their study.

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R. Anderson, S. Ekstrom, C. Georgy, et. al.
Wed, 5 Mar 14
6/75

Radial and vertical flows induced by galactic spiral arms: likely contributors to our "wobbly Galaxy'' [GA]

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http://arxiv.org/abs/1403.0587


In an equilibrium axisymmetric galactic disc, the mean galactocentric radial and vertical velocities are expected to be zero everywhere. In recent years, various large spectroscopic surveys have however shown that stars of the Milky Way disc exhibit non-zero mean velocities outside of the Galactic plane in both the Galactocentric radial and vertical velocity components. While radial velocity structures are commonly assumed to be associated with non-axisymmetric components of the potential such as spiral arms or bars, non-zero vertical velocity structures are usually attributed to excitations by external sources such as a passing satellite galaxy or a small dark matter substructure crossing the Galactic disc. Here, we use a three-dimensional test-particle simulation to show that the global stellar response to a spiral perturbation induces both a radial velocity flow and non-zero vertical motions. The resulting structure of the mean velocity field is qualitatively similar to what is observed across the Milky Way disc. We show that such a pattern also naturally emerges from an analytic toy model based on linearized Euler equations. We conclude that an external perturbation of the disc might not be a requirement to explain all of the observed structures in the vertical velocity of stars across the Galactic disc. Non-axisymmetric internal perturbations can also be the source of the observed mean velocity patterns.

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C. Faure, A. Siebert and B. Famaey
Wed, 5 Mar 14
8/75

Identification of old tidal dwarfs near early-type galaxies from deep imaging and HI observations [CEA]

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http://arxiv.org/abs/1403.0626


It has recently been proposed that the dwarf spheroidal galaxies located in the Local Group disks of satellites (DoSs) may be tidal dwarf galaxies (TDGs) born in a major merger at least 5 Gyr ago. Whether TDGs can live that long is still poorly constrained by observations. As part of deep optical and HI surveys with the CFHT MegaCam camera and Westerbork Synthesis Radio Telescope made within the ATLAS3D project, and follow-up spectroscopic observations with the Gemini-North telescope, we have discovered old TDG candidates around several early-type galaxies. At least one of them has an oxygen abundance close to solar, as expected for a tidal origin. This confirmed pre-enriched object is located within the gigantic, but very low surface brightness, tidal tail that emanates from the elliptical galaxy, NGC 5557. An age of 4 Gyr estimated from its SED fitting makes it the oldest securely identified TDG ever found so far. We investigated the structural and gaseous properties of the TDG and of a companion located in the same collisional debris, and thus most likely of tidal origin as well. Despite several Gyr of evolution close to their parent galaxies, they kept a large gas reservoir. Their central surface brightness is low and their effective radius much larger than that of typical dwarf galaxies of the same mass. This possibly provides us with criteria to identify tidal objects which can be more easily checked than the traditional ones requiring deep spectroscopic observations. In view of the above, we discuss the survival time of TDGs and question the tidal origin of the DoSs.

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P. Duc, S. Paudel, R. McDermid, et. al.
Wed, 5 Mar 14
10/75

Probing non-standard gravity with the growth index: a background independent analysis [CEA]

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http://arxiv.org/abs/1403.0898


Measurements of the growth index $\gamma(z)$ provide a clue as to whether Einstein’s field equations encompass gravity also on large cosmic scales, those where the expansion of the universe accelerates. We show that the information encoded in this function can be satisfactorily parameterized using a small set of coefficients $\gamma_i$ in such a way that the true scaling of the growth index is recovered to better than $1\%$ in most dark energy and dark gravity models. We find that the likelihood of current data is maximal for $\gamma_0=0.74\pm 0.44$ and $\gamma_1=0.01\pm0.46$, a measurement compatible with the $\Lambda$CDM predictions. Moreover data favor models predicting slightly less growth of structures than the Planck LambdaCDM scenario. The main aim of the paper is to provide a prescription for routinely calculating, in an analytic way, the amplitude of the growth indices $\gamma_i$ in relevant cosmological scenarios, and to show that these parameters naturally define a space where predictions of alternative theories of gravity can be compared against growth data in a manner which is independent from the expansion history of the cosmological background. As the standard $\Omega$-plane provides a tool to identify different expansion histories $H(t)$ and their relation to various cosmological models, the $\gamma$-plane can thus be used to locate different growth rate histories $f(t)$ and their relation to alternatives model of gravity. As a result, we find that the Dvali-Gabadadze-Porrati gravity model is rejected with a $95\%$ confidence level. By simulating future data sets, such as those that a Euclid-like mission will provide, we also show how to tell apart LambdaCDM predictions from those of more extreme possibilities, such as smooth dark energy models, clustering quintessence or parameterized post-Friedmann cosmological models.

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H. Steigerwald, J. Bel and C. Marinoni
Wed, 5 Mar 14
12/75

Cluster X-ray line at $3.5\,{\rm keV}$ from axion-like dark matter [CEA]

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http://arxiv.org/abs/1403.0865


The recently reported X-ray line signal at $E_\gamma \simeq 3.5 {\rm keV}$ from a stacked spectrum of various galaxy clusters and Andromeda galaxy may be originated from a decaying dark matter particle of the mass $2 E_\gamma$. A light axion-like scalar is suggested as a natural candidate for dark matter and its production mechanisms are closely examined. We show that the right amount of axion relic density with the preferred parameters, $m_a \simeq 7 {\rm keV}$ and $f_a \simeq 4\times 10^{14} {\rm GeV}$, is naturally obtainable from the decay of inflaton or saxion decay. The small misalignment angles of the axion, $\theta_a\sim 10^{-4} -10^{-1}$, depending on the reheating temperature, can be also the source of axion production. The model satisfies the constraints required for structure formation and iso-curvature perturbation.

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H. Lee, S. Park and W. Park
Wed, 5 Mar 14
15/75

Diffuse Ly$α$ Halos around Galaxies at $z=2.2-6.6$: Implications for Galaxy Formation and Cosmic Reionization [CEA]

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http://arxiv.org/abs/1403.0732


We present diffuse Ly$\alpha$ halos (LAHs) identified in the composite Subaru narrowband images of $100-3600 $ Ly$\alpha$ emitters (LAEs) at $z=2.2$, $3.1$, $3.7$, $5.7$, and $6.6$. First, we carefully examine potential artifacts mimicking LAHs that include a large-scale point-spread function (PSF) made by instrumental and atmospheric effects. Based on our critical test with composite images of non-LAE samples whose narrowband-magnitude and source-size distributions are the same as our LAE samples, we confirm that no artifacts can produce a diffuse extended feature similar to our LAHs. After this test, we measure the scale lengths of exponential profile for the LAHs estimated from our $z=2.2-6.6$ LAE samples of $L_{\rm Ly\alpha}\gtrsim 2\times 10^{42}$ erg s$^{-1}$. We obtain the scale lengths of $\simeq 5-10$ kpc at $z=2.2-5.7$, and find no evolution of scale lengths in this redshift range beyond our measurement uncertainties. Combining this result and the previously-known UV-continuum size evolution, we infer that the ratio of LAH to UV-continuum sizes is nearly constant at $z=2.2-5.7$. On the other hand, the scale length of our $z=6.6$ LAH is larger than $5-10$ kpc, and there is a hint that the scale lengths of LAHs would increase from $z=5.7$ to $6.6$. This may be a signature of increasing fraction of neutral hydrogen scattering Ly\alpha$ photons, due to cosmic reionization, although larger data are needed for a definitive conclusion.

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R. Momose, M. Ouchi, K. Nakajima, et. al.
Wed, 5 Mar 14
16/75

Emergent Lorentz Signature, Fermions, and the Standard Model [CL]

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http://arxiv.org/abs/1403.0580


This article investigates the construction of fermions and the formulation of the Standard Model of particle physics in a theory in which the Lorentz signature emerges from an underlying microscopic purely Euclidean $SO(4)$ theory. Couplings to a clock field are responsible for triggering the change of signature of the effective metric in which the standard fields propagate. We demonstrate that Weyl and Majorana fermions can be constructed in this framework. This construction differs from other studies of Euclidean fermions, as the coupling to the clock field allows us to write down an action which flows to the usual action in Minkowski spacetime. We then show how the Standard Model can be obtained in this theory and consider the constraints on non-Standard Model operators which can appear in the QED sector, due to CPT and Lorentz violation.

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J. Kehayias, S. Mukohyama and J. Uzan
Wed, 5 Mar 14
26/75

Fossil Groups Origins III. Characterization of the sample and observational properties of fossil systems [CEA]

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http://arxiv.org/abs/1403.0588


(Abridged) Fossil systems are group- or cluster-sized objects whose luminosity is dominated by a very massive central galaxy. In the current cold dark matter scenario, these objects formed hierarchically at an early epoch of the Universe and then slowly evolved until present day. That is the reason why they are called {\it fossils}. We started an extensive observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Deep $r-$band images were taken for each candidate and optical spectroscopic observations were obtained for $\sim$ 1200 galaxies. This new dataset was completed with SDSS DR7 archival data to obtain robust cluster membership and global properties of each fossil group candidate. For each system, we recomputed the magnitude gaps between the two brightest galaxies ($\Delta m_{12}$) and the first and fourth ranked galaxies ($\Delta m_{14}$) within 0.5 $R_{{\rm 200}}$. We consider fossil systems those with $\Delta m_{12} \ge 2$ mag or $\Delta m_{14} \ge 2.5$ mag within the errors. We find that 15 candidates turned out to be fossil systems. Their observational properties agree with those of non-fossil systems. Both follow the same correlations, but fossils are always extreme cases. In particular, they host the brightest central galaxies and the fraction of total galaxy light enclosed in the central galaxy is larger in fossil than in non-fossil systems. Finally, we confirm the existence of genuine fossil clusters. Combining our results with others in the literature, we favor the merging scenario in which fossil systems formed due to mergers of $L^\ast$ galaxies. The large magnitude gap is a consequence of the extreme merger ratio within fossil systems and therefore it is an evolutionary effect. Moreover, we suggest that at least one candidate in our sample could represent a transitional fossil stage.

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S. Zarattini, R. Barrena, M. Girardi, et. al.
Wed, 5 Mar 14
32/75

Deep R-band counts of z~3 Lyman break galaxy candidates with the LBT [CEA]

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http://arxiv.org/abs/1403.0727


Aims. We present a deep multiwavelength imaging survey (UGR) in 3 different fields, Q0933, Q1623, and COSMOS, for a total area of ~1500arcmin^2. The data were obtained with the Large Binocular Camera on the Large Binocular Telescope. Methods. To select our Lyman break galaxy (LBG) candidates, we adopted the well established and widely used color-selection criterion (U-G vs. G-R). One of the main advantages of our survey is that it has a wider dynamic color range for U-dropout selection than in previous studies. This allows us to fully exploit the depth of our R-band images, obtaining a robust sample with few interlopers. In addition, for 2 of our fields we have spectroscopic redshift information that is needed to better estimate the completeness of our sample and interloper fraction. Results. Our limiting magnitudes reach 27.0(AB) in the R band (5\sigma) and 28.6(AB) in the U band (1\sigma). This dataset was used to derive LBG candidates at z~3. We obtained a catalog with a total of 12264 sources down to the 50% completeness magnitude limit in the R band for each field. We find a surface density of ~3 LBG candidates arcmin^2 down to R=25.5, where completeness is >=95% for all 3 fields. This number is higher than the original studies, but consistent with more recent samples.

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K. Boutsia, A. Grazian, E. Giallongo, et. al.
Wed, 5 Mar 14
38/75

The 2XMMi/SDSS Galaxy Cluster Survey. III. Clusters associated with spectroscopically targeted luminous red galaxies in SDSS-DR10 [CEA]

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http://arxiv.org/abs/1403.0758


We present a sample of 383 X-ray selected galaxy groups and clusters with spectroscopic redshift measurements (up to z ~ 0.79) from the 2XMMi/SDSS Galaxy Cluster Survey. The X-ray cluster candidates were selected as serendipitously detected sources from the 2XMMi-DR3 catalogue that were located in the footprint of the Sloan Digital Sky Survey (SDSS-DR7). The cluster galaxies with available spectroscopic redshifts were selected from the SDSS-DR10. We developed an algorithm for identifying the cluster candidates that are associated with spectroscopically targeted luminous red galaxies and for constraining the cluster spectroscopic redshift. A cross-correlation of the constructed cluster sample with published optically selected cluster catalogues yielded 264 systems with available redshifts. The present redshift measurements are consistent with the published values. The current cluster sample extends the optically confirmed cluster sample from our cluster survey by 67 objects. Moreover, it provides spectroscopic confirmation for 78 clusters among our published cluster sample, which previously had only photometric redshifts. Of the new cluster sample that comprises 67 systems, 55 objects are newly X-ray discovered clusters and 52 systems are sources newly discovered as galaxy clusters in optical and X-ray wavelengths. Based on the measured redshifts and the fluxes given in the 2XMMi-DR3 catalogue, we estimated the X-ray luminosities and masses of the cluster sample.

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A. Takey, A. Schwope and G. Lamer
Wed, 5 Mar 14
39/75

A Medieval Multiverse: Mathematical Modelling of the 13th Century Universe of Robert Grosseteste [CL]

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http://arxiv.org/abs/1403.0769


In his treatise on light, written in about 1225, Robert Grosseteste describes a cosmological model in which the Universe is created in a big-bang like explosion and subsequent condensation. He postulates that the fundamental coupling of light and matter gives rises to the material body of the entire cosmos. Expansion is arrested when matter reaches a minimum density and subsequent emission of light from the outer region leads to compression and rarefaction of the inner bodily mass so as to create nine celestial spheres, with an imperfect residual core. In this paper we reformulate the Latin description in terms of a modern mathematical model. The equations which describe the coupling of light and matter are solved numerically, subject to initial conditions and critical criteria consistent with the text. Formation of a universe with a non-infinite number of perfected spheres is extremely sensitive to the initial conditions, the intensity of the light and the transparency of these spheres. In this “medieval multiverse”, only a small range of opacity and initial density profiles lead to a stable universe with nine perfected spheres. As in current cosmological thinking, the existence of Grosseteste’s universe relies on a very special combination of fundamental parameters.

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R. Bower, T. S%2E, B. Tanner, et. al.
Wed, 5 Mar 14
40/75

Evolution in the bias of faint radio sources to z ~ 2.2 [CEA]

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http://arxiv.org/abs/1403.0882


Quantifying how the baryonic matter traces the underlying dark matter distribution is key to both understanding galaxy formation and our ability to constrain the cosmological model. Using the cross-correlation function of radio and near-infrared galaxies, we present a large-scale clustering analysis of radio galaxies to z ~ 2.2. We measure the angular auto-correlation function of Ks < 23.5 galaxies in the VIDEO-XMM3 field with photometric redshifts out to z = 4 using VIDEO and CFHTLS photometry in the near-infrared and optical. We then use the cross-correlation function of these sources with 766 radio sources at S_1.4 > 90 {\mu}Jy to infer linear bias of radio galaxies in four redshift bins. We find that the bias evolves from b = 0.57 +/- 0.06 at z ~ 0.3 to 8.55 +/- 3.11 at z ~ 2.2. Furthermore, we separate the radio sources into subsamples to determine how the bias is dependent on the radio luminosity, and find a bias which is significantly higher than predicted by the simulations of Wilman et al., and consistent with the lower luminosity but more abundant FR-I population having a similar bias to the highly luminous but rare FR-IIs. Our results are suggestive of a higher mass, particularly for FR-I sources than assumed in simulations, especially towards higher redshift.

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S. Lindsay, M. Jarvis and K. McAlpine
Wed, 5 Mar 14
42/75

The Atacama Cosmology Telescope: Cross Correlation with Planck maps [CEA]

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http://arxiv.org/abs/1403.0608


We present the temperature power spectrum of the Cosmic Microwave Background obtained by cross-correlating maps from the Atacama Cosmology Telescope (ACT) at 148 and 218 GHz with maps from the Planck satellite at 143 and 217 GHz, in two overlapping regions covering 592 square degrees. We find excellent agreement between the two datasets at both frequencies, quantified using the variance of the residuals between the ACT power spectra and the ACTxPlanck cross-spectra. We use these cross-correlations to calibrate the ACT data at 148 and 218 GHz, to 0.7% and 2% precision respectively. We find no evidence for anisotropy in the calibration parameter. We compare the Planck 353 GHz power spectrum with the measured amplitudes of dust and cosmic infrared background (CIB) of ACT data at 148 and 218 GHz. We also compare planet and point source measurements from the two experiments.

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T. Louis, G. Addison, M. Hasselfield, et. al.
Wed, 5 Mar 14
43/75

Probing Modified Gravity Theories with ISW and CMB Lensing [CEA]

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http://arxiv.org/abs/1403.0852


The imprint of the cross-correlation of the Integrated Sachs-Wolfe effect (ISW) and lensing of the cosmic microwave background (CMB) radiation has recently been detected in the bispectrum of temperature maps. In this paper, we use the optimised skew-spectrum as well as skew-spectra associated with Minkowski Functionals (MFs) to test the possibility of using this signal to detect deviations in the theory of gravity away from General Relativity (GR). We find that the although both statistics can put constraints on modified gravity, the optimised skew-spectra are especially sensitive to the parameter $\rB_0$ that denotes the the {\em Compton wavelength} of the scalaron at the present epoch, and both can be used to put stringent constraints on any departure from GR, or pinpoint any systematics in the data. We investigate three modified gravity theories, namely: the Post-Parametrised Friedmanian (PPF) formalism; the Hu-Sawicki (HS) model; and the Bertschinger-Zukin (BZ) formalism. Employing a likelihood analysis for an experimental setup similar to ESA’s Planck mission, we find that, assuming GR to be the correct model, we expect the constraints from the first two skew-spectra, $S_{\ell}^{(0)}$ and $S_{\ell}^{(1)}$, to be the same: $\rm B_0<0.45$ at $95\%$ confidence level (CL), and $\rm B_0<0.67$ at $99\%$ CL in the BZ model. The third skew-spectrum does not give any meaningful constraint. The performance of MFs can be improved by using Wiener-type filtering, but we find that the optimal skew-spectrum is much more powerful, giving $\rm B_0<0.071$ at $95\%$ CL and $\rm B_0<0.15$ at $99\%$ CL, which is a factor of six improvement compared to constraints derived from MF, and essentially identical to what can be achieved using the full bispectrum.

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D. Munshi, B. Hu, A. Renzi, et. al.
Wed, 5 Mar 14
48/75

Larson's scaling laws, and the gravitational instability of clumpy discs at high redshift [GA]

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http://arxiv.org/abs/1403.0799


Gravitational instabilities play a primary role in shaping the clumpy structure and powering the star formation activity of gas-rich high-redshift galaxies. Here we analyse the stability of such systems, focusing on the size and mass ranges of unstable regions in the disc. Our analysis takes into account the mass-size and linewidth-size scaling relations observed in molecular gas, originally discovered by Larson. We show that such relations can have a strong impact on the size and mass of star-forming clumps, as well as on the stability properties of the disc at all observable scales, making the classical Toomre parameter a highly unreliable indicator of gravitational instability. For instance, a disc with Q=1 can be far from marginal instability, while a disc with Q<<1 can be marginally unstable. Our work raises an important caveat: if clumpy discs at high redshift have scale-dependent surface densities and velocity dispersions, as implied by the observed clump scaling relations, then we cannot thoroughly understand their stability and star formation properties unless we perform multi-scale observations. This will soon be possible thanks to dedicated ALMA surveys, which will explore the physical properties of super-giant molecular clouds at the peak of cosmic star formation and beyond.

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A. Romeo and O. Agertz
Wed, 5 Mar 14
49/75

Inflamagnetogenesis redux: Unzipping inflection-point inflation via various cosmoparticle probes [CL]

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http://arxiv.org/abs/1403.0676


In this paper I introduce a precise constraint on primordial magnetogenesis, for a generic class of single-field inflection point inflationary model followed by small field excursion below the Planck scale. I also establish a connection between the magnetic field at the present epoch and primordial gravity waves ($r$) via non-vanishing CP asymmetry parameter ($\epsilon_{\bf CP}$), which triggers the leptogenesis scenario. Finally, I explore various hidden cosmophenomenological features of theoretical CMB B-mode polarization spectra, which can be treated as a significant probe to put further stringent constraint on low and high scale inflection point inflationary models after releasing the Planck B-mode polarization data.

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S. Choudhury
Wed, 5 Mar 14
51/75

Gas reservoir of a hyper-luminous QSO at z=2.6 [GA]

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http://arxiv.org/abs/1403.0853


Understanding the relationship between the formation and evolution of galaxies and their central super massive black holes (SMBH) is one of the main topics in extragalactic astrophysics. Links and feedback may reciprocally affect both black hole and galaxy growth. Observations of the CO line at redshifts of 2-4 are crucial to investigate the gas mass, star formation activity and accretion onto SMBHs, as well as the effect of AGN feedback. Potential correlations between AGN and host galaxy properties can be highlighted by observing extreme objects. Despite their luminosity, hyper-luminous QSOs at z=2-4 are still little studied at mm wavelengths. We targeted CO(3-2) in ULAS J1539+0557, an hyper-luminos QSO (Lbol> 10^48 erg/s) at z=2.658, selected through its unusual red colors in the UKIDSS Large Area Survey (ULAS). We find a molecular gas mass of 4.1+-0.8 10^10 Msun, and a gas fraction of 0.4-0.1, depending mostly on the assumed source inclination. We also find a robust lower limit to the star-formation rate (SFR=250-1600 Msun/yr) and star-formation efficiency (SFE=25-350 Lsun/(K km s-1 pc2) by comparing the observed optical-near-infrared spectral energy distribution with AGN and galaxy templates. The black hole gas consumption timescale, M(H_2)/dM(accretion)/dt, is ~160 Myr, similar or higher than the gas consumption timescale. The gas content and the star formation efficiency are similar to those of other high-luminosity, highly obscured QSOs, and at the lower end of the star-formation efficiency of unobscured QSOs, in line with predictions from AGN-galaxy co-evolutionary scenarios. Further measurements of the (sub)-mm continuum in this and similar sources are mandatory to obtain a robust observational picture of the AGN evolutionary sequence.

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C. Feruglio, A. Bongiorno, F. Fiore, et. al.
Wed, 5 Mar 14
53/75

The Premature Formation of High Redshift Galaxies [CEA]

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http://arxiv.org/abs/1403.0908


Observations with WFC3/IR on the Hubble Space Telescope and the use of gravitational lensing techniques have facilitated the discovery of galaxies as far back as z ~ 10-12, a truly remarkable achievement. However, this rapid emergence of high-z galaxies, barely ~ 200 Myr after the transition from Population III star formation to Population II, appears to be in conflict with the standard view of how the early Universe evolved. This problem has much in common with the better known (and probably related) premature appearance of supermassive black holes at z ~ 6. It is difficult to understand how ~ 10^9 solar-mass black holes could have appeared so quickly after the big bang without invoking non-standard accretion physics and the formation of massive seeds, neither of which is seen in the local Universe. In earlier work, we showed that the appearance of high-z quasars could instead be understood more reasonably in the context of the R_h=ct Universe, which does not suffer from the same time compression issues as LCDM does at early epochs. Here, we build on that work by demonstrating that the evolutionary growth of primordial galaxies was consistent with the current view of how the first stars formed, but only with the timeline afforded by the R_h=ct cosmology. We also show that the growth of high-z quasars was mutually consistent with that of the earliest galaxies, though it is not yet clear whether the former grew from 5-20 solar-mass seeds created in Population III or Population II supernova explosions.

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F. Melia
Wed, 5 Mar 14
63/75

CLASH: Extending galaxy strong lensing to small physical scales with distant sources highly-magnified by galaxy cluster members [CEA]

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http://arxiv.org/abs/1403.0573


We present a strong lensing system in which a double source is imaged 5 times by 2 early-type galaxies. We take advantage in this target of the multi-band photometry obtained as part of the CLASH program, complemented by the spectroscopic data of the VLT/VIMOS and FORS2 follow-up campaign. We use a photometric redshift of 3.7 for the source and confirm spectroscopically the membership of the 2 lenses to the galaxy cluster MACS J1206.2-0847 at redshift 0.44. We exploit the excellent angular resolution of the HST/ACS images to model the 2 lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersions of (97 +/- 3) and (240 +/- 6) km/s. The total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, that is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to our best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of about (1.0 +/- 0.5) x 10^{9} M_{Sun}. By combining the total and luminous mass estimates of the 2 lenses, we measure luminous over total mass fractions projected within the effective radii of 0.51 +/- 0.21 and 0.80 +/- 0.32. With these lenses we can extend the analysis of the mass properties of lens early-type galaxies by factors that are about 2 and 3 times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of our lenses with those of astrophysical objects with different physical scales reveals the potential of studies of this kind for investigating the internal structure of galaxies. These studies, made possible thanks to the CLASH survey, will allow us to go beyond the current limits posed by the available lens samples in the field.

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C. Grillo, R. Gobat, V. Presotto, et. al.
Wed, 5 Mar 14
65/75

First experimental constraints on the disformally-coupled Galileon model [CL]

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http://arxiv.org/abs/1403.0854


The Galileon model is a modified gravity model that can explain the late-time accelerated expansion of the Universe. In a previous work, we derived experimental constraints on the Galileon model with no explicit coupling to matter, and showed that this model agrees with the most recent cosmological data. In the context of braneworld constructions or massive gravity, the Galileon model exhibits a disformal coupling to matter which we study in this paper. After comparing our constraints on the uncoupled model with recent studies, we extend the analysis framework to the disformally-coupled Galileon model and derive the first experimental constraints on that coupling, using precise measurements of cosmological distances and the growth rate of cosmic structures. In the uncoupled case, with updated data, we still observe a small tension between the constraints set by growth data and those from distances. In the disformally-coupled Galileon model, we obtain a better agreement with data, and favour a non-zero disformal coupling to matter at the $2.5\sigma$ level. This gives an interesting hint on possible braneworld origin of Galileon theory.

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J. Neveu, V. Ruhlmann-Kleider, P. Astier, et. al.
Wed, 5 Mar 14
66/75

Representing the Graviton Self-Energy on de Sitter Background [CL]

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http://arxiv.org/abs/1403.0896


We derive a noncovariant but simple representation for the self-energy of a conformally transformed graviton field on the cosmological patch of de Sitter. Our representation involves four structure functions, as opposed to the two that would be necessary for a manifestly de Sitter invariant representation. We work out what the four structure functions are for the one loop correction due to a massless, minimally coupled scalar. And we employ the result to work out what happens to dynamical gravitons.

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K. Leonard, S. Park, T. Prokopec, et. al.
Wed, 5 Mar 14
69/75

Baryonic matter perturbations in decaying vacuum cosmology [CEA]

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http://arxiv.org/abs/1403.0427


We consider the perturbation dynamics for the cosmic baryon fluid and determine the corresponding power spectrum for a $\Lambda(t)$CDM model in which a cosmological term decays into dark matter linearly with the Hubble rate. The model is tested by a joint analysis of data from supernovae of type Ia (SNIa) (Constitution and Union 2.1), baryonic acoustic oscillation (BAO), the position of the first peak of the anisotropy spectrum of the cosmic microwave background (CMB) and large-scale-structure (LSS) data (SDSS DR7). While the homogeneous and isotropic background dynamics is only marginally influenced by the baryons, there are modifications on the perturbative level if a separately conserved baryon fluid is included. Considering the present baryon fraction as a free parameter, we reproduce the observed abundance of the order of $5\%$ independently of the dark-matter abundance which is of the order of $32\%$ for this model. Generally, the concordance between background and perturbation dynamics is improved if baryons are explicitly taken into account.

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R. Marttens, W. Hipolito-Ricaldi and W. Zimdahl
Tue, 4 Mar 14
7/61

Imaging the environment of a z = 6.3 submillimeter galaxy with SCUBA-2 [CEA]

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http://arxiv.org/abs/1403.0247


We describe a search for submillimeter emission in the vicinity of one of the most distant, luminous galaxies known, HerMES FLS3 at z=6.34, exploiting it as a signpost to a potentially biased region of the early Universe, as might be expected in hierarchical structure formation models. Imaging to the confusion limit with the innovative, wide-field submillimeter bolometer camera, SCUBA-2, we are sensitive to colder and/or less luminous galaxies in the surroundings of HFLS3. We use the Millennium Simulation to illustrate that HFLS3 may be expected to have companions if it is as massive as claimed, but find no significant evidence from the surface density of SCUBA-2 galaxies in its vicinity, or their colors, that HFLS3 marks an over-density of dusty, star-forming galaxies. We cannot rule out the presence of dusty neighbours with confidence, but deeper 450-um imaging has the potential to more tightly constrain the redshifts of nearby galaxies, at least one of which likely lies at z>~5. If associations with HFLS3 can be ruled out, this could be taken as evidence that HFLS3 is less biased than a simple extrapolation of the Millennium Simulation may imply. This could suggest either that it represents a rare short-lived, but highly luminous, phase in the evolution of an otherwise typical galaxy, or that this system has suffered amplification due to a foreground gravitational lens and so is not as intrinsically luminous as claimed.

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E. Robson, R. Ivison, I. Smail, et. al.
Tue, 4 Mar 14
13/61

Isospin-Violating Dark Matter with Colored Mediators [CL]

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http://arxiv.org/abs/1403.0324


In light of positive signals reported by the CDMS-II Si experiment and the recent results of the LUX and SuperCDMS experiments, we study isospin-violating dark matter scenarios assuming that the interaction of the dark matter is mediated by colored particles. We investigate the phenomenology of the model, including collider searches, flavor and CP phenomenology. A minimal possible scenario includes scalar dark matter and new vector-like colored fermions with masses of O(1) TeV as mediators. Such a scenario may be probed at the 14 TeV LHC, while flavor and CP constraints are stringent and severe tuning in the couplings is unavoidable. We also found that, as an explanation of the CDMS-II Si signal, isospin-violating fermionic dark matter models with colored scalar mediators are disfavored by the LHC constraints.

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K. Hamaguchi, S. Liew, T. Moroi, et. al.
Tue, 4 Mar 14
17/61

Scalar-Tensor Gravity Cosmology: Noether symmetries and analytical solutions [CEA]

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http://arxiv.org/abs/1403.0332


In this paper, we present a complete Noether Symmetry analysis in the framework of scalar-tensor cosmology. Specifically, we consider a non-minimally coupled scalar field action embedded in the FLRW spacetime and provide a full set of Noether symmetries for related minisuperspaces. The presence of symmetries implies that the dynamical system becomes integrable and then we can compute cosmological analytical solutions for specific functional forms of coupling and potential functions selected by the Noether Approach.

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A. Paliathanasis, M. Tsamparlis, S. Basilakos, et. al.
Tue, 4 Mar 14
20/61

Probing reionization using quasar near-zones at redshift z ~ 6 [CEA]

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http://arxiv.org/abs/1403.0221


Using hydrodynamical simulations coupled to a 1D radiative transfer code, we study the additional heating effects produced by $z\sim6$ QSOs in their near-zones. We show that both normalization ($T_0$) and slope ($\gamma$) of the intergalactic medium (IGM) effective equation-of-state get modified by the excess ionization from the quasars. However, the extent of this effect depends on the physical conditions prevailing in the IGM prior to the quasar era. We show, with a sample size similar to the presently available data, that it will be relatively easier to detect the change in $T_0$ compared to that in $\gamma$. Using the available constraints on $T_0$ at $z\sim6$, we discuss implications for the nature and epoch of HI and HeII reionization. We study the extent of He III region as a function of quasar age and show, for a typical inferred age of $z\sim6$ QSOs (i.e $\sim 10^8$ yrs), it extends up to 80 per cent of the HI proximity region. This is also the time-scale over which the temperature in most of the near-zone saturates and becomes distance independent. This implies that even when one uses all the HI lines in the QSO proximity region, the heating effects can be detected as long as the QSO age is sufficiently large. Using flux and curvature probability distribution functions (pdfs), we study the statistical detectability of heating effects as a function of initial physical conditions prevailing in the IGM. We show that for the present sample size, cosmic variance dominates the flux pdf. The curvature statistics is more suited to capturing the heating effects beyond the cosmic variance, even if the sample size is half of what is presently available.

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H. Padmanabhan, T. Choudhury and R. Srianand
Tue, 4 Mar 14
23/61

The Role of Feedback in Shaping the Structure of the Interstellar Medium [GA]

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http://arxiv.org/abs/1403.0488


We present an analysis of the role of feedback in shaping the neutral hydrogen (HI) content of simulated disc galaxies. For our analysis, we have used two realisations of two separate Milky Way-like (~L*) discs – one employing a conservative feedback scheme (MUGS), the other significantly more energetic (MaGICC). To quantify the impact of these schemes, we generate zeroth moment (surface density) maps of the inferred HI distribution; construct power spectra associated with the underlying structure of the simulated cold ISM, in addition to their radial surface density and velocity dispersion profiles. Our results are compared with a parallel, self-consistent, analysis of empirical data from THINGS (The HI Nearby Galaxy Survey). Single power-law fits (P~k^gamma) to the power spectra of the stronger-feedback (MaGICC) runs (over spatial scales corresponding to 0.5 kpc to 20 kpc) result in slopes consistent with those seen in the THINGS sample (gamma = -2.5). The weaker-feedback (MUGS) runs exhibit shallower power law slopes (gamma = -1.2). The power spectra of the MaGICC simulations are more consistent though with a two-component fit, with a flatter distribution of power on larger scales (i.e., gamma = -1.4 for scales in excess of 2 kpc) and a steeper slope on scales below 1 kpc (gamma = -5), qualitatively consistent with empirical claims, as well as our earlier work on dwarf discs. The radial HI surface density profiles of the MaGICC discs show a clear exponential behaviour, while those of the MUGS suite are essentially flat; both behaviours are encountered in nature, although the THINGS sample is more consistent with our stronger (MaGICC) feedback runs.

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A. Walker, B. Gibson, K. Pilkington, et. al.
Tue, 4 Mar 14
25/61

Exploring the Intergalactic Magnetic Field by Means of Faraday Tomography [CEA]

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http://arxiv.org/abs/1403.0325


Unveiling the intergalactic magnetic field (IGMF) in filaments of galaxies is a very important and challenging subject in modern astronomy. In order to probe the IGMF from rotation measures (RMs) of extragalactic radio sources, we need to separate RMs due to other origins such as the source, intervening galaxies, and our Galaxy. In this paper, we discuss observational strategies for the separation by means of Faraday tomography (Faraday RM Synthesis). We consider an observation of a single radio source such as a radio galaxy or a quasar viewed through the Galaxy and the cosmic web. We then compare the observation with another observation of a neighbor source with a small angular separation. Our simulations with simple models of the sources suggest that it would be not easy to detect the RM due to the IGMF of order ~ 1 rad/m/m, an expected value for the IGMF through a single filament. Contrary to it, we find that the RM of at least ~10 rad/m/m could be detected with the SKA or its pathfinders/precursors, if we achieve selections of ideal sources. These results would be improved if we incorporate decomposition techniques such as RMCLEAN and QU-fitting. We discuss feasibility of the strategies for cases with complex Galactic emissions as well as with effects of observational noise and radio frequency interferences.

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T. Akahori, K. Kumazaki, K. Takahashi, et. al.
Tue, 4 Mar 14
30/61

Cosmic Star Formation History [CEA]

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http://arxiv.org/abs/1403.0007


Over the last decade and a half, an avalanche of new data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Making sense of it all and fitting it together into a coherent picture remains one of astronomy’s great challenges. Here we review the range of complementary techniques and theoretical tools that are allowing astronomers to map the cosmic history of star formation, heavy element production, and reionization of the universe from the cosmic “dark ages” to the present epoch. A consistent picture is emerging from modern galaxy surveys, whereby the star formation rate density peaked about 3.5 Gyr after the Big Bang, at redshift 1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before redshift 1.3. Less than 1% of today’s stars formed during the epoch of reionization, at redshift greater than 6. Under the simple assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star formation activity, although a mild disagreement may still point to unresolved issues with the measurements, or to deviations in the stellar initial mass function from conventional assumptions. The assembly histories of the stellar component of galaxies and their central black holes were quite similar, offering evidence for the co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the universe to about 0.001 solar by redshift six, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological deionization.

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P. Madau and M. Dickinson
Tue, 4 Mar 14
32/61

Non-linear matter bispectrum in general relativity [CEA]

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http://arxiv.org/abs/1403.0438


We show that the relativistic effects are negligibly small in the non-linear density and velocity bispectra. Although the non-linearities of Einstein equation introduce additional non-linear terms to the Newtonian fluid equations, the corrections to the bispectrum only show up on super-horizon scales. We show this with the next-to-leading order non-linear bispectrum for a pressureless fluid in a flat Friedmann-Robertson-Walker background, by calculating the density and velocity fields up to fourth order. We work in the comoving gauge, where the dynamics is identical to the Newtonian up to second order. We also discuss the leading order matter bispectrum in various gauges, and show yet another relativistic effect near horizon scales that the matter bispectrum strongly depends on the gauge choice.

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S. Biern, J. Gong and D. Jeong
Tue, 4 Mar 14
33/61

Satellites of Radio AGN in SDSS: Insights into AGN Triggering and Feedback [CEA]

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http://arxiv.org/abs/1403.0003


We study the effects of radio jets on galaxies in their vicinity (satellites) and the role of satellites in triggering radio-loud active galactic nuclei (AGNs). The study compares the aggregate properties of satellites of a sample of 7,220 radio AGNs at z < 0.3 (identified by Best & Heckman 2012 from the SDSS and NVSS+FIRST surveys) to the satellites of a control sample of radio-quiet galaxies, which are matched in redshift, color, luminosity, and axis ratio, as well as by environment type: field galaxies, cluster members and brightest cluster galaxies (BCGs). Remarkably, we find that radio AGNs exhibit on average a 50% excess (17{\sigma} significance) in the number of satellites within 100 kpc even though the cluster membership was controlled for (e.g., radio BCGs have more satellites than radio-quiet BCGs, etc.). Satellite excess is not confirmed for high-excitation sources, which are only 2% of radio AGN. Extra satellites may be responsible for raising the probability for hot gas AGN accretion via tidal effects or may otherwise enhance the intensity or duration of the radio-emitting phase. Furthermore, we find that the incidence of radio AGNs among potential hosts (massive ellipticals) is similar for field galaxies and for non-BCG cluster members, suggesting that AGN fueling depends primarily on conditions in the host halo rather than the parent, cluster halo. Regarding feedback, we find that radio AGNs, either high or low excitation, have no detectable effect on star formation in their satellites, as neither induced star formation nor star formation quenching is present in more than ~1% of radio AGN.

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C. Pace and S. Salim
Tue, 4 Mar 14
38/61

Evidence for a gas-rich major merger in a proto-cluster at z=2.5 [GA]

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http://arxiv.org/abs/1403.0040


We present a deep Jansky Very Large Array observation of CO J=1-0 emission line in a proto-cluster at z=2.53, USS1558-003. The target field is an especially dense region, where 20 H-alpha emitters (HAEs) are clustering. We successfully detect CO emission lines from four HAEs and give an upper limit for 16 HAEs. Red, massive star-forming galaxies tend to be gas rich while blue less massive galaxies are faint in the CO emission. Given the close proximity (32 kpc), small velocity offset (130 km/s), and similar stellar masses of the two CO emitters, ID 191 and ID 193, they could be in the phase prior to a gas-rich major merger. ID 193 shows a red color in the rest-frame optical, suggesting the presence of dusty star-formation. Using MIPS 24 um and radio continuum images, we find a total infrared luminosity of L(IR)=5.1e12 Lsun for ID 193, corresponding to SFR~880 Msun/yr. The L(IR)/L'(CO) ratio is significantly enhanced compared to local spirals/high-redshift disks at a fixed CO luminosity, which is indicative of a starburst mode. Our results suggest that ID 193 lies in the late stage of merger where violent star formation is induced by a past interaction with a gas-rich galaxy but the neighboring blue HAE, ID 191. The most intriguing result is that such a system is discovered in an extremely dense region at z>2. The formation processes of slow rotators seen in local massive clusters may involve such multiple gas-rich mergers in proto-clusters at z>2.

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K. Tadaki, T. Kodama, Y. Tamura, et. al.
Tue, 4 Mar 14
39/61

First measurement of $σ_8$ using supernova data only [CEA]

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http://arxiv.org/abs/1403.0293


A method was recently proposed which allows the conversion of the weak-lensing effects in the supernova Hubble diagram from noise into signal. Such signal is sensitive to the growth of structure in the universe, and in particular can be used as a measurement of $\sigma_8$ which is independent from more traditional methods such as those based on the CMB, cosmic shear or cluster abundance. We extend here that analysis to allow for intrinsic non-Gaussianities in the supernova PDF, and discuss how this can be best modelled using the Bayes Factor. Although it was shown that a precise measurement of $\sigma_8$ requires ~$10^5$ supernovae, current data already allows an important proof of principle. In particular we make use of the 732 supernovae with z < 1 of the recent JLA catalog and show that a simple treatment of intrinsic non-Gaussianities with a couple of nuisance parameters is enough for our method to yield the values $\sigma_8 = 0.84^{+0.28}_{-0.65}$ or $\sigma_8 < 1.45$ at a $2\sigma$ confidence level. This result is consistent with mock simulations and it is also in agreement with independent measurements and presents the first ever measurement of $\sigma_8$ using supernova data alone.

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T. Castro and M. Quartin
Tue, 4 Mar 14
44/61

Axion Hilltop Inflation in Supergravity [CL]

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http://arxiv.org/abs/1403.0410


We show that the recently proposed multi-natural inflation can be realized within the framework of 4D ${\cal N}=1$ supergravity. The inflaton potential mainly consists of two sinusoidal potentials that are comparable in size, but have different periodicity with a possible non-zero relative phase. For a sub-Planckian decay constant, the multi-natural inflation model is reduced to axion hilltop inflation. We show that, taking into account the effect of the relative phase, the spectral index can be increased to give a better fit to the Planck results, with respect to the hilltop quartic inflation. We also consider a possible UV completion based on a string-inspired model. Interestingly, the Hubble parameter during inflation is necessarily smaller than the gravitino mass, avoiding possible moduli destabilization. Reheating processes as well as non-thermal leptogenesis are also discussed.

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M. Czerny, T. Higaki and F. Takahashi
Tue, 4 Mar 14
46/61

Quintessence reconstruction of interacting HDE in a non-flat universe [CEA]

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http://arxiv.org/abs/1403.0196


In this paper we consider quintessence reconstruction of interacting holographic dark energy in a non-flat background. As system’s IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as $L=ar(t)$. To this end we construct a quintessence model by a real, single scalar field. Evolution of the potential, $V(\phi)$, as well as the dynamics of the scalar field, $\phi$, are obtained according to the respective holographic dark energy. The reconstructed potentials show a cosmological constant behavior for the present time. We constrain the model parameters in a flat universe by using the observational data, and applying the Monte Carlo Markov chain simulation. We obtain the best fit values of the holographic dark energy model and the interacting parameters as $c=1.0576^{+0.3010+0.3052}_{-0.6632-0.6632}$ and $\zeta=0.2433^{+0.6373+0.6373}_{-0.2251-0.2251}$, respectively. From the data fitting results we also find that the model can cross the phantom line in the present universe where the best fit value of of the dark energy equation of state is $w_D=-1.2429$.

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A. Sheykhi, H. Alavirad, A. Bagheri, et. al.
Tue, 4 Mar 14
56/61

A physical model for the evolving UV luminosity function of high redshift galaxies and their contribution to the cosmic reionization [CEA]

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http://arxiv.org/abs/1403.0055


[Abridged] We present a physical model for the evolution of the ultraviolet (UV) luminosity function (LF) of high-z galaxies taking into account in a self-consistent way their chemical evolution and the associated evolution of dust extinction. The model yields good fits of the UV and Lyman-alpha LFs at z>~2. The weak evolution of both LFs between z=2 and z=6 is explained as the combined effect of the negative evolution of the halo mass function, of the increase with redshift of the star formation efficiency, and of dust extinction. The slope of the faint end of the UV LF is found to steepen with increasing redshift, implying that low luminosity galaxies increasingly dominate the contribution to the UV background at higher and higher redshifts. The observed range of UV luminosities at high-z implies a minimum halo mass capable of hosting active star formation M_crit <~ 10^9.8 M_odot, consistent with the constraints from hydrodynamical simulations. From fits of Lyman-alpha LFs plus data on the luminosity dependence of extinction and from the measured ratios of non-ionizing UV to Lyman-continuum flux density for samples of z=~3 Lyman break galaxies and Lyman-alpha emitters, we derive a simple relationship between the escape fraction of ionizing photons and the star formation rate, impling larger escape fraction for less massive galaxies. Galaxies already represented in the UV LF (M_UV <~ -18) can keep the universe fully ionized up to z=~6, consistent with (uncertain) data pointing to a rapid drop of the ionization degree above z~6. On the other side, the electron scattering optical depth, tau_es, inferred from CMB experiments favor an ionization degree close to unity up to z=~9-10. Consistency with CMB data can be achieved if M_crit =~ 10^8.5 M_odot, implying that the UV LFs extend to M_UV =~ -13, although the corresponding tau_es is still on the low side of CMB-based estimates.

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Z. Cai, A. Lapi, A. Bressan, et. al.
Tue, 4 Mar 14
57/61

Exhausting the Information: Novel Bayesian Combination of Photometric Redshift PDFs [CEA]

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http://arxiv.org/abs/1403.0044


The estimation and utilization of photometric redshift (photo-z) PDFs has become increasingly important over the last few years. Primarily this is because of the prominent role photo-z PDFs play in enabling photometric survey data to be used to make cosmological constraints, especially when compared to single estimates. Currently there exist a wide variety of algorithms to compute photo-z’s, each with their own strengths and weaknesses. In this paper, we present a novel and efficient Bayesian framework that combines the results from different photo-z techniques into a more powerful and robust estimate by maximizing the information from the photometric data. To demonstrate this we use a supervised machine learning technique based on prediction trees and a random forest, an unsupervised method based on self organizing maps and a random atlas, and a standard template fitting method but can be easily extend to other existing techniques. We use data from the DEEP2 survey and more than $10^6$ galaxies from the SDSS to explore different methods for combining the photo-z predictions from these techniques. In addition, we demonstrate that we can improve the accuracy of our final photo-z estimate over the best input technique, that the fraction of outliers is reduced, and that the identification of outliers is significantly improved when we apply a Na\”ive Bayes Classifier to this combined information. Furthermore, we introduce a new approach to explore how different techniques perform across the different areas within the information space supported by the photometric data. Our more robust and accurate photo-z PDFs will allow even more precise cosmological constraints to be made by using photometric surveys. These improvements are crucial as we move to analyze photometric data that push to or even past the limits of the available training data, which will be the case with the LSST.

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M. Kind and R. Brunner
Tue, 4 Mar 14
60/61

Universe acceleration in modified gravities: $F(R)$ and $F(T)$ cases [CL]

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http://arxiv.org/abs/1402.7114


We review recent progress on cosmological issues and theoretical properties of modified gravity theories. In particular, we explicitly explore the conformal transformation, the Starobinsky inflation, and a unified scenario of inflation and late time acceleration in $F(R)$ gravity and $F(T)$ gravity (extended teleparallel gravity). Furthermore, we examine neutron stars and the hyperon problem in $F(R)$ gravity. Moreover, for loop quantum cosmology (LQC), the natures of finite-time future singularities in $F(T)$ gravity are presented. In addition, we investigate $F(T)$ gravity theories from the Kaluza-Klein (KK) and Randall-Sundrum (RS) theories.

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K. Bamba and S. Odintsov
Mon, 3 Mar 14
1/55

Observational Signatures of Binary Supermassive Black Holes [HEAP]

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http://arxiv.org/abs/1402.7098


Observations indicate that most massive galaxies contain a supermassive black hole, and theoretical studies suggest that when such galaxies have a major merger, the central black holes will form a binary and eventually coalesce. Here we discuss two spectral signatures of such binaries that may help distinguish them from ordinary AGN. These signatures are expected when the mass ratio between the holes is not extreme and the system is fed by a circumbinary disk. One such signature is a notch in the thermal continuum that has been predicted by other authors; we point out that it should be accompanied by a spectral revival at shorter wavelengths and also discuss its dependence on binary properties such as mass, mass ratio, and separation. In particular, we note that the wavelength $\lambda_n$ at which the notch occurs depends on these three parameters in such a way as to make the number of systems displaying these notches $\propto \lambda_n^{16/3}$; longer wavelength searches are therefore strongly favored. A second signature, first discussed here, is hard X-ray emission with a Wien-like spectrum at a characteristic temperature $\sim 100$ keV produced by Compton cooling of the shock generated when streams from the circumbinary disk hit the accretion disks around the individual black holes. We investigate the observability of both signatures. The hard X-ray signal may be particularly valuable as it can provide an indicator of black hole merger a few decades in advance of the event.

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C. Roedig, J. Krolik and M. Miller
Mon, 3 Mar 14
3/55

Cold dark matter haloes in the Planck era: evolution of structural parameters for Einasto and NFW profiles [CEA]

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http://arxiv.org/abs/1402.7073


We present the evolution of the structure of relaxed cold dark matter haloes in the cosmology from the Planck satellite. Our simulations cover 5 decades in halo mass, from dwarf galaxies to galaxy clusters. Due to the increased matter density and power spectrum normalization the concentration mass relation in the Planck cosmology has a 20 percent higher normalization at redshift z=0 compared to WMAP cosmology. We confirm that CDM haloes are better described by the Einasto profile; for example, at scales near galaxy half-light radii CDM haloes have significantly steeper density profiles than implied by NFW fits. There is a scatter of 0.2 dex in the Einasto shape parameter at fixed halo mass, adding further to the diversity of CDM halo profiles. The evolution of the concentration mass relation in our simulations is not reproduced by any of the analytic models in the literature. We thus provide a simple fitting formula that accurately describes the evolution between redshifts z=5 to z=0 for both NFW and Einasto fits. Finally, the observed concentrations and halo masses at low redshifts of spiral galaxies, groups and clusters of galaxies are in good agreement with our simulations, suggesting only mild halo response on these scales.

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A. Dutton and A. Maccio
Mon, 3 Mar 14
5/55

Narrow Polar Rings versus Wide Polar Ring/Diks Galaxies [GA]

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http://arxiv.org/abs/1402.7325


In the latest ten years, a big effort has given to study the morphology and kinematics of polar ring galaxies: many steps forward and new discoveries on the structure and formation mechanisms for such systems have been made during this time thanks to high resolution photometric and spectroscopic data. In this paper, I review the latest results obtained for this class of galaxies, from both observational and theoretical studies. I focus on the analysis of the observed properties (e.g., structure, colours, age, metallicity, and kinematics) for narrow and wide polar ring galaxies. In particular, I compare AM2020-504 and NGC4650A, which are the two prototypes for narrow and wide polar rings, respectively. I discuss similarities and differences between the two kinds of systems and how they reconcile with the main formation scenarios proposed for this class of galaxies.

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E. Iodice
Mon, 3 Mar 14
8/55

A 3.55 keV hint for decaying axion-like particle dark matter [CL]

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http://arxiv.org/abs/1402.7335


Recently, indications for an emission line at 3.55 keV have been found in the combined spectra of a large number of galaxy clusters and also in Andromeda. This line could not be identified with any known spectral line. It is tempting to speculate that it has its origin in the decay of a particle contributing all or part of the dark matter. In this note we want to point out that axion-like particles being all or part of the dark matter are an ideal candidate to produce such a feature. More importantly the parameter values necessary are quite feasible in extensions of the Standard Model based on string theory and could be linked up to a variety of other intriguing phenomena, which also potentially allow for new tests of this speculation.

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J. Jaeckel, J. Redondo and A. Ringwald
Mon, 3 Mar 14
13/55

Asymptotically Lifshitz black hole solutions in F(R) gravity [CL]

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http://arxiv.org/abs/1309.2135


We consider a class of spherically symmetric spacetime to obtain some interesting solutions in F(R) gravity without matter field (pure gravity). We investigate the geometry of the solutions and find that there is an essential singularity at the origin. In addition, we show that there is an analogy between obtained solutions with the black holes of Einstein-Lambda -power-Maxwell-invariant theory. Furthermore, we find that these solutions are equivalent to the asymptotically Lifshitz black holes. Also, we calculate d^2F/dR^2 to examine the Dolgov-Kawasaki stability criterion.

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S. Hendi, B. Panah and C. Corda
Mon, 3 Mar 14
17/55

Type Ia Supernova Colors and Ejecta Velocities: Hierarchical Bayesian Regression with Non-Gaussian Distributions [CEA]

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http://arxiv.org/abs/1402.7079


We investigate the correlations between the peak intrinsic colors of Type Ia supernovae (SN Ia) and their expansion velocities at maximum light, measured from the Si II 6355 A spectral feature. We construct a new hierarchical Bayesian regression model and Gibbs sampler to estimate the dependence of the intrinsic colors of a SN Ia on its ejecta velocity, while accounting for the random effects of intrinsic scatter, measurement error, and reddening by host galaxy dust. The method is applied to the apparent color data from BVRI light curves and Si II velocity data for 79 nearby SN Ia. Comparison of the apparent color distributions of high velocity (HV) and normal velocity (NV) supernovae reveals significant discrepancies in B-V and B-R, but not other colors. Hence, they are likely due to intrinsic color differences originating in the B-band, rather than dust reddening. The mean intrinsic B-V and B-R color differences between HV and NV groups are 0.06 +/- 0.02 and 0.09 +/- 0.02 mag, respectively. Under a linear model for intrinsic B-V and B-R colors versus velocity, we find significant slopes of -0.021 +/- 0.006 and -0.030 +/- 0.009 mag/(1000 km/s), respectively. Since the ejecta velocity distribution is skewed towards high velocities, these effects imply non-Gaussian intrinsic color population distributions with skewness up to +0.3. Accounting for the intrinsic color-velocity correlation results in corrections in A_V extinction estimates as large as -0.12 mag for HV SN Ia and +0.06 mag for NV events. Deviance information criteria strongly favor simple functions for intrinsic colors versus velocity over no trend, while higher-order polynomials are disfavored. Velocity measurements from SN Ia spectra have potential to diminish systematic errors from the confounding of intrinsic colors and dust reddening affecting supernova distances.

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K. Mandel, R. Foley and R. Kirshner
Mon, 3 Mar 14
19/55

Quantum transitions of minimum energy for Hawking quanta in highly excited black holes: problems for loop quantum gravity? [CL]

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http://arxiv.org/abs/1212.0746


By analysing some recent results by Yoon, which arise from loop quantum gravity and from the assumption of the locality of photon emission in a black hole, we argue that they are not consistent with our recent semi-classical results for highly excited black holes. Maybe that the results by Yoon can be correct for non-highly excited black holes, but, in any case, our analysis renders further problematical the match between loop quantum gravity and semi-classical theory.

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C. Corda
Mon, 3 Mar 14
20/55

Salpeter normalization of the Stellar Initial Mass Function for massive galaxies at z~1 [CEA]

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http://arxiv.org/abs/1402.7354


The stellar initial mass function (IMF) is a key parameter to study galaxy evolution. Here we measure the IMF mass normalization for a sample of 68 field galaxies in the redshift range 0.7 to 0.9 within the Extended Groth Strip. To do this we derive total (stellar + dark matter) mass-to-light [$(M/L)_{\rm dyn}$] using axisymmetric dynamical models. Within the region where we have kinematics (about one half-light radius), the models assume: (i) that mass-follows-light, implying negligible differences between the stellar and total density profiles; (ii) constant velocity anisotropy ($\beta_{\rm z}\equiv1-\sigma_z^2/\sigma_R^2=0.2$); (iii) that galaxies are seen at the average inclination for random orientations (i.e. $i=60^\circ$, where $i=90^\circ$ represents edge-on). The dynamical models are based on anisotropic Jeans equations, constrained by HST/ACS imaging and the central velocity dispersion of the galaxies, extracted from good-quality spectra taken by the DEEP2 survey. The population $(M/L)_{\rm pop}$ are derived from full-spectrum fitting of the same spectra with a grid of simple stellar population models. Recent dynamical modelling results by the $ATLAS^{3D}$ project and numerical simulations of galaxy evolution indicate that the dark matter fraction within the central regions of our galaxies should be small. This suggest that our derived total $(M/L)_{\rm dyn}$ should closely approximate the stellar $M/L$. Our comparison of $(M/L)_{\rm dyn}$ and $(M/L)_{\rm pop}$ then imply that for galaxies with stellar mass $M_\odot \geq 10^{11}$ $M_{\odot}$, the $average$ normalization of the IMF is consistent with a Salpeter slope, with a substantial scatter. This is similar to what is found within a similar mass range for nearby galaxies.

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S. Shetty and M. Cappellari
Mon, 3 Mar 14
22/55

Non-strictly black body spectrum from the tunnelling mechanism [CL]

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http://arxiv.org/abs/1305.4529


A modern and largely used approach to obtain Hawking radiation is the tunnelling mechanism. However, in various papers in the literature, the analysis concerned almost only to obtain the Hawking temperature through a comparison of the probability of emission of an outgoing particle with the Boltzmann factor. In a interesting and well written paper, Banerjee and Majhi improved the approach, by explicitly finding a black body spectrum associated with black holes. On the other hand, this result, which has been obtained by using a reformulation of the tunnelling mechanism, is in contrast which the remarkable result by Parikh and Wilczek, that, indeed, found a probability of emission which is compatible with a non-strictly thermal spectrum. By using our recent introduction of an effective state for a black hole, here we solve such a contradiction, through a slight modification of the analysis by Banerjee and Majhi. The final result will be a non-strictly black body spectrum from the tunnelling mechanism. We also show that, for an effective temperature, we can write the corresponding effective metric by Hawking’s periodicity arguments. Potential important implications for the black hole information puzzle are also discussed

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C. Corda
Mon, 3 Mar 14
28/55

Dark Energy and Dark Matter like intrinsic curvature in extended gravity. Viability through gravitational waves [CL]

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http://arxiv.org/abs/1211.1373


Towards the goal to quantize gravity, in this short review we discuss an intermediate step which consists in extending the picture of standard General Relativity by considering Extended Theories of Gravity. In this tapestry, the equations to quantize are not the standard Einstein field equations of General Relativity, but the extended Einstein field equations of such Extended Theories. The traditional relation between mass-energy and space-time curvature, which founds standard General Relativity, results modified in this new picture and, at least at the linearized approximation, variations of the space-time curvature generate the mass-energy. Various problems of the Dark Universe, Dark Energy, Dark Matter and Pioneer anomaly, can be, in principle, solved through this approach, while a definitive endorsement for Extended Theories of Gravity could arrive from the realization of a consistent gravitational wave astronomy. We also discuss the quantization of both mass-energy and space-time curvature in the early Universe by using the process of amplification of vacuum fluctuations which is connected with the primordial production of relic gravitational waves. A future detection of such relic gravitational waves will be an ultimate endorsement for the quantum rather than classical feature of the gravitational interaction.

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C. Corda
Mon, 3 Mar 14
37/55

The Mass-Independence of Specific Star Formation Rates in Galactic Disks [CEA]

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http://arxiv.org/abs/1402.7076


The slope of the star formation rate/stellar mass relation (the SFR “Main Sequence”; SFR–Mstel) is not quite unity: specific star formation rates (SFR/Mstel) are weakly-but-significantly anti-correlated with Mstel. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions — portions of a galaxy not forming stars — with Mstel. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFRd = SFR/Mdisk) reduces the Mstel-dependence of SF efficiency by ~0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log(sSFRd)–log(Mstel) to have a slope -0.20 < beta_disk < 0.00 +/- 0.02 (depending on SFR estimator and Main Sequence definition) for star-forming galaxies with Mstel > 10^10 Msun and bulge mass-fractions B/T < 0.7, generally consistent with a pure-disk control sample (beta_control = -0.05 +/- 0.04). That <SFR/Mdisk> is (largely) independent of host mass for star-forming disks bears strongly on scenarios of galaxy evolution derived from any SFR–Mstel relation, including: the principal manifestation of “mass quenching” (bulge growth); the constancy of the shape of the star-forming stellar mass function (uniform dlog(Mstel)/dt, assuming disk-driven growth); and the degree to which dispersion in SFR(Mstel,t) encodes diversity in star formation histories. Our results emphasize the need to treat galaxies as composite systems — not integrated masses — in observational and theoretical work.

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L. Abramson, D. Kelson, A. Dressler, et. al.
Mon, 3 Mar 14
38/55

Black hole quantum spectrum [CL]

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http://arxiv.org/abs/1210.7747


Introducing a black hole (BH) effective temperature, which takes into account both the non-strictly thermal character of Hawking radiation and the countable behavior of emissions of subsequent Hawking quanta, we recently re-analysed BH quasi-normal modes (QNMs) and interpreted them naturally in terms of quantum levels. In this work we improve such an analysis removing some approximations that have been implicitly used in our previous works and obtaining the corrected expressions for the formulas of the horizon’s area quantization and the number of quanta of area and hence also for Bekenstein-Hawking entropy, its sub-leading corrections and the number of micro-states, i.e. quantities which are fundamental to realize the underlying quantum gravity theory, like functions of the QNMs quantum “overtone” number n and, in turn, of the BH quantum excited level. An approximation concerning the maximum value of n is also corrected. On the other hand, our previous results were strictly corrected only for scalar and gravitational perturbations. Here we show that the discussion holds also for vector perturbations. The analysis is totally consistent with the general conviction that BHs result in highly excited states representing both the “hydrogen atom” and the “quasi-thermal emission” in quantum gravity. Our BH model is somewhat similar to the semi-classical Bohr’s model of the structure of a hydrogen atom. The thermal approximation of previous results in the literature is consistent with the results in this paper. In principle, such results could also have important implications for the BH information paradox.

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C. Corda
Mon, 3 Mar 14
39/55

Search for Low-Mass WIMPs with SuperCDMS [CL]

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http://arxiv.org/abs/1402.7137


We report a first search for weakly interacting massive particles (WIMPs) using the background rejection capabilities of SuperCDMS. An exposure of 577 kg-days was analyzed for WIMPs with mass < 30 GeV/c2, with the signal region blinded. Eleven events were observed after unblinding. We set an upper limit on the spin-independent WIMP-nucleon cross section of 1.2e-42 cm2 at 8 GeV/c2. This result is in tension with WIMP interpretations of recent experiments and probes new parameter space for WIMP-nucleon scattering for WIMP masses < 6 GeV/c2.

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R. Agnese, A. Anderson, M. Asai, et. al.
Mon, 3 Mar 14
40/55

Too fast for chaotic, too slow for coherent: the missing link between accretion, massive black hole spins and galaxy kinematics [CEA]

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http://arxiv.org/abs/1402.7088


We present the results of a semianalytical model that evolves the masses and spins of massive black holes together with the properties of their host galaxies along the cosmic history. As a consistency check, our model broadly reproduces a number of observations, e.g. the cosmic star formation history, the black hole mass and luminosity function and the galaxy mass function at low redshift, the black hole to bulge mass relation, and the morphological distribution at low redshift. For the first time in a semianalytical investigation, we relax the simplifying assumptions of perfect coherency or perfect isotropy of the gas fueling the black holes. The dynamics of gas is instead linked to the morphological properties of the host galaxies, resulting in different spin distributions for black holes hosted in different galaxy types. We compare our results with the observed sample of spin measurements obtained through broad K-alpha iron line fitting. The observational data disfavor both accretion along a fixed direction and isotropic fueling. Conversely, when the properties of the accretion flow are anchored to the kinematics of the host galaxy, we obtain a good match between theoretical expectations and observations. A mixture of coherent accretion and phases of activity in which the gas dynamics is similar to that of the stars in bulges (i.e., with a significant velocity dispersion superimposed to a net rotation) best describes the data, adding further evidence in support to the coevolution of massive black holes and their hosts.

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A. Sesana, E. Barausse, M. Dotti, et. al.
Mon, 3 Mar 14
42/55

Time-Dependent Schrodinger Equation for Black Hole Evaporation: no Information Loss [CL]

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http://arxiv.org/abs/1304.1899


In 1976 S. Hawking claimed that “Because part of the information about the state of the system is lost down the hole, the final situation is represented by a density matrix rather than a pure quantum state” (Verbatim from ref. 2.) This was the starting point of the popular “black hole (BH) information paradox”. On the other hand, during one of his famous quantum field theory lectures at Harvard, S. Coleman claimed that “The career of a young theoretical physicist consists of treating the harmonic oscillator in ever-increasing levels of abstraction.” One of the highest levels of abstraction concerning the harmonic oscillator in Nature is surely represented by BH quasi-normal modes (QNMs), which are a countable set of damped oscillations representing the BH’s reaction to perturbations. In a series of papers, together with collaborators, I naturally interpreted BH QNMs in terms of quantum levels. Here I explicitly write down a time dependent Schr\”odinger equation for the system composed by Hawking radiation and BH QNMs. The physical state and the correspondent wave-function are written in terms of an unitary evolution matrix instead of a density matrix. Thus, the final state results to be a pure quantum state instead of mixed one. Hence, Hawking’s claim is falsified by an application of Coleman’s claim. Information comes out in BH evaporation in terms of pure states in an unitary time dependent evolution. The assumption by ‘t Hooft that Schr\”oedinger equations can be used universally for all dynamics in the universe is in turn confirmed, further endorsing the conclusion that BH evaporation must be information preserving.

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C. Corda
Mon, 3 Mar 14
44/55

VLBA Observations of Mrk 6: Probing the Jet-Lobe Connection [GA]

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http://arxiv.org/abs/1402.7174


We present the results of high resolution VLBI observations at 1.6 and 4.9 GHz of the radio-loud Seyfert galaxy, Mrk 6. These observations are able to detect a compact radio core in this galaxy for the first time. The core has an inverted spectral index ($\alpha^{1.6}_{4.9}$=+1.0$\pm$0.2) and a brightness temperature of $1\times10^8$ K. Three distinct radio components which resemble jet elements and/or hot spots, are also detected. The position angles of these elongated jet elements point, not only to a curved jet in Mrk 6, but also towards a connection between the AGN and the kpc-scale radio lobes/bubbles in this galaxy. Firmer constraints on the star formation rate provided by new Herschel observations (SFR $<0.8$ M$_\sun$ yr$^{-1}$) make the starburst-wind powered bubble scenario implausible. From plasma speeds obtained via prior Chandra X-ray observations, and ram pressure balance arguments for the ISM and radio bubbles, the north-south bubbles are expected to take $7.5\times10^6$ yr to form, and the east-west bubbles $1.4\times10^6$ yr. We suggest that the jet axis has changed at least once in Mrk 6 within the last $\approx10^7$ yr. A comparison of the nuclear radio-loudness of Mrk 6 and a small sample of Seyfert galaxies with a subset of low-luminosity FRI radio galaxies reveals a continuum in radio properties.

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P. Kharb, C. ODea, S. Baum, et. al.
Mon, 3 Mar 14
45/55

Effective state, Hawking radiation and quasi-normal modes for Kerr black holes [CL]

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http://arxiv.org/abs/1305.3710


The non-strictly continuous character of the Hawking radiation spectrum generates a natural correspondence between Hawking radiation and black hole (BH) quasi-normal modes (QNM). In this work, we generalize recent results on this important issue to the framework of Kerr BHs (KBH). We show that also for the KBH, QNMs can be naturally interpreted in terms of quantum levels. Thus, the emission or absorption of a particle is in turn interpreted in terms of a transition between two different levels. At the end of the paper, we also generalize some concepts concerning the “effective state” of a KBH.

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C. Corda, S. Hendi, R. Katebi, et. al.
Mon, 3 Mar 14
46/55

Constraints on Light Magnetic Dipole Dark Matter from the ILC and SN 1987A [CL]

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http://arxiv.org/abs/1402.7295


To illustrate the complementarity of the linear collider and astrophysics bounds on the light (MeV-scale mass) dark matter (DM), we study the constraints on the magnetic dipole DM from the DM-electron interactions at the proposed International Linear Collider (ILC) and in supernova (SN) 1987A. We in particular focus on the $e^+ e^-$ annihilation which is the common process for producing DM pairs both at the ILC and in the SN. We estimate the bounds on the DM magnetic dipole moment from the mono-photon signals at the ILC and also from the energy loss rate due to the freely streaming DM produced in the SN. The SN bounds can be more stringent than those from the ILC by as much as a factor ${\cal O}(10^5)$ for a DM mass below $10^2$ MeV. For larger DM masses, on the other hand, SN rapidly loses its sensitivity and the collider constraints can complement the SN constraints.

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K. Kadota and J. Silk
Mon, 3 Mar 14
48/55

The source-lens clustering effect in the context of lensing tomography and its self-calibration [CEA]

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http://arxiv.org/abs/1402.7144


(Abridged) Sampling the cosmic shear field through observation is inevitably biased, since cosmic shear can only be measured where there are galaxies and the galaxy distribution is correlated with the lensing signal. This source-lens clustering (SLC) effect has two sources, intrinsic source clustering and cosmic magnification (magnification/size bias). The former decreases with decreasing width of the source galaxy redshift distribution. However, this reduction is limited. Hence it remains unclear whether the residual can be controlled below the statistical error of stage IV lensing surveys. Furthermore, SLC induced by cosmic magnification can not be reduced by lensing tomography. Through N-body simulations, we quantify the impact of SLC on lensing E/B-mode power spectrum in the context of lensing tomography. We consider two favorite estimators in measuring the lensing power spectrum, standard estimator and pixel-based estimator. We find that none of the two estimators can satisfactorily handle both sources of SLC. For standard estimator, SLC induced by both the two sources can bias the lensing power spectrum by O(1%)-O(10%) and the exact value depends on the galaxy bias and the flux/size of source galaxies. SLC induced by intrinsic source clustering also increases statistical uncertainties in the measured lensing power spectrum. However, standard estimator suppresses intrinsic source clustering induced SLC in cross power spectrum. In contrast, pixel-based estimator is efficient to suppress SLC induced by cosmic magnification. However, it fails to suppress SLC induced by intrinsic source clustering and the measured lensing power spectrum can be biased low by O(1%)-O(10%). We conclude that SLC effect is a severe systematic error for weak lensing cosmology, even with the aid of lensing tomography. We present useful scaling relations to self-calibrate SLC effect.

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Y. Yu, P. Zhang, W. Lin, et. al.
Mon, 3 Mar 14
51/55

The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching [CEA]

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http://arxiv.org/abs/1402.7077


We investigate the velocity vs. position phase space of z ~ 1 cluster galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from the GCLASS survey. Dividing the galaxy population into three categories: quiescent, star-forming, and poststarburst, we find that these populations have distinct distributions in phase space. Most striking are the poststarburst galaxies, which are commonly found at small clustercentric radii with high clustercentric velocities, and appear to trace a coherent “ring” in phase space. Using several zoom simulations of clusters we show that the coherent distribution of the poststarbursts can be reasonably well-reproduced using a simple quenching scenario. Specifically, the phase space is best reproduced if satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a total time of ~ 1 Gyr after first infall. We compare this quenching timescale to the timescale implied by the stellar populations of the poststarburst galaxies and find that the poststarburst spectra are well-fit by a rapid quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy. The similarity between the quenching timescales derived from these independent indicators is a strong consistency check of the quenching model. Given that the model implies satellite quenching is rapid, and occurs well within R_{200}, this would suggest that ram-pressure stripping of either the hot or cold gas component of galaxies are the most plausible candidates for the physical mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to determine if hot or cold gas stripping is dominant; however, measurements of the redshift evolution of the satellite quenching timescale and location may be capable of distinguishing between the two.

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A. Muzzin, R. Burg, S. McGee, et. al.
Mon, 3 Mar 14
52/55

Cosmology and gravitational waves in the Nordstrom-Vlasov system, a laboratory for Dark Energy [CL]

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http://arxiv.org/abs/1301.5900


We discuss a cosmological solution of the system which was originally introduced by Calogero and is today popularly known as “Nordstrom-Vlasov system”. Although the model is un-physical, its cosmological solution results interesting for the same reasons for which the Nordstrom-Vlasov system was originally introduced in the framework of galactic dynamics. In fact, it represents a theoretical laboratory where one can rigorously study some problems, like the importance of the gravitational waves in the dynamics, which at the present time are not well understood within the physical model of the Einstein-Vlasov system. As the cosmology of the Nordstrom-Vlasov system is founded on a scalar field, a better understanding of the system is important also in the framework of the Dark Energy problem. In fact, various attempts to achieve Dark Energy by using scalar fields are present in the literature. In the solution an analytical expression for the time dependence of the cosmological evolution of the Nordstrom’s scalar field is also released.This analytical expression is unknown in the literature of the Nordstrom-Vlasov system. Based on their importance, the propagation of gravitational waves in the Nordstrom-Vlasov system and their effects on test masses are also discussed.

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C. Corda
Mon, 3 Mar 14
54/55

Lensing Model of MACS J1149.5+2223 I: Cluster Mass Reconstruction [CEA]

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http://arxiv.org/abs/1402.7321


Measurements of the total logarithmic central slope of the mass profile in galaxy clusters constrain their evolution and assembly history and that of their Brightest Cluster Galaxies. We report the first full surface brightness distribution modelling of the inner region of the galaxy cluster MACS J1149.5+2223. We compare these results with a position-based modelling approach for which we employ more than twice the previously known positional constraints. This is the first time that the detailed lensed image configuration of two non-central cluster galaxies with Einstein rings has been mapped. Due to the extended radial coverage provided by the multiple images in this system, we are able to determine the slope $\partial \log{\kappa}/\partial \log{R} = -0.37$ of the total projected mass distribution from $8$ to $80 \mathrm{kpc}$. This is within the cluster-to-cluster scatter estimates from previous cluster measurements. Our reconstruction of the image surface brightness distribution of the large central spiral galaxy has a root mean square residual for all image pixels of $1.14 \sigma$, where $\sigma$ is the observational background noise. This corresponds to a reconstruction of the positions of bright clumps in the central galaxy with a rms of $0.063 \mathrm{arcseconds}$.

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S. Rau, S. Vegetti and S. White
Mon, 3 Mar 14
55/55

Dense plasma dispersion of Fast radio bursts [CEA]

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http://arxiv.org/abs/1402.7068


Stellar coronae have been invoked to explain the apparently extragalactic dispersion measures observed in Fast radio bursts (Loeb, Shvartzvald & Maoz 2014). This paper demonstrates that the suggested plasma densities would lead to deviations from the standard dispersion curve that are inconsistent with the data and likely rule out the model independently of the argument of Luan (2014). The problem is then turned around and higher-order dispersion terms are connected to the moments of the density distribution along the line of sight. The deviations quantified in three observed bursts are analysed and a lower limit on the maximum electron density is obtained in one case, although with considerable uncertainty. Selection effects are then discussed and shown to be non-restrictive in relation to plasma density, except at the lowest frequencies.

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A. Tuntsov
Fri, 28 Feb 14
3/54