The ALHAMBRA survey: 2-D analysis of the stellar populations in massive early-type galaxies at z < 0.3 [GA]

We present a technique that permits the analysis of stellar population gradients in a relatively low cost way compared to IFU surveys analyzing a vastly larger samples as well as out to larger radii. We developed a technique to analyze unresolved stellar populations of spatially resolved galaxies based on photometric multi-filter surveys. We derived spatially resolved stellar population properties and radial gradients by applying a Centroidal Voronoi Tesselation and performing a multi-color photometry SED fitting. This technique has been applied to a sample of 29 massive (M${\star}$ > 10$^{10.5}$ M${\odot}$), early-type galaxies at $z$ < 0.3 from the ALHAMBRA survey. We produced detailed 2D maps of stellar population properties (age, metallicity and extinction). Radial structures have been studied and luminosity-weighted and mass-weighted gradients have been derived out to 2 – 3.5 R$\mathrm{eff}$. We find the gradients of early-type galaxies to be on average flat in age ($\nabla$log Age$\mathrm{L}$ = 0.02 $\pm$ 0.06 dex/R$\mathrm{eff})$ and negative in metallicity ($\nabla$[Fe/H]$\mathrm{L}$ = – 0.09 $\pm$ 0.06 dex/R$\mathrm{eff}$). Overall, the extinction gradients are flat ($\nabla$A$\mathrm{v}$ = – 0.03 $\pm$ 0.09 mag/R$_\mathrm{eff}$ ) with a wide spread. These results are in agreement with previous studies that used standard long-slit spectroscopy as well as with the most recent integral field unit (IFU) studies. According to recent simulations, these results are consistent with a scenario where early-type galaxies were formed through major mergers and where their final gradients are driven by the older ages and higher metallicity of the accreted systems. We demonstrate the scientific potential of multi-filter photometry to explore the spatially resolved stellar populations of local galaxies and confirm previous spectroscopic trends from a complementary technique.

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I. Roman, A. Cenarro, L. Diaz-Garcia, et. al.
Wed, 26 Jul 17

Comments: 25 pages, 18 figures, accepted for publication in A&A

Galaxy And Mass Assembly (GAMA): The mechanisms for quiescent galaxy formation at $z<1$ [GA]

One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the GAMA and VIPERS surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies. We identify potentially rapidly transitioning post-starburst galaxies, and slower transitioning green-valley galaxies. Over the last 8 Gyrs the quiescent population has grown more slowly in number density at high masses (M$*>10^{11}$M$\odot$) than at intermediate masses (M$*>10^{10.6}$M$\odot$). There is evolution in both the post-starburst and green valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times. At intermediate masses (M$*>10^{10.6}$M$\odot$) we find a green valley transition timescale of 2.6 Gyr. Alternatively, at $z\sim0.7$ the entire growth rate could be explained by fast-quenching post-starburst galaxies, with a visibility timescale of 0.5 Gyr. At lower redshift, the number density of post-starbursts is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at $z<1$. However, at high masses (M$*>10^{11}$M$\odot$), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high mass post-starburst and green-valley galaxies are transitioning from star-forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation.

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K. Rowlands, V. Wild, N. Bourne, et. al.
Wed, 26 Jul 17

Comments: 19 pages, 11 figures, 3 tables. Accepted for publication in MNRAS

The dipole anisotropy of WISE x SuperCOSMOS number counts [CEA]

We probe the validity of the isotropy hypothesis of the Universe, one of the foundations of modern Cosmology, with the WISE $\times$ SuperCOSMOS data set. This is performed by searching for dipole anisotropy of galaxy number counts in different redshift shells in the $0.10 < z \leq 0.35$ range. We find that the dipole direction is in concordance with most of previous analyses in the literature, however, its amplitude is only consistent with $\Lambda$CDM-based mocks when we adopt the cleanest sample of this catalogue, except for the $z < 0.15$ data, which exhibits a persistently large dipole signal. Hence, we obtain no significant evidence against the large-scale isotropy assumption once the data are purified from stellar contamination, yet our results in the lowest redshift range are still inconclusive.

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C. Bengaly, C. Novaes, H. Xavier, et. al.
Wed, 26 Jul 17

Comments: 5 pages, 4 figures, 2 tables. Comments welcome!

Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization [GA]

We present a new method to quantify the value of the escape fraction of ionizing photons, and the existence of ultra-faint galaxies clustered around brighter objects during the epoch of cosmic reionization, using the diffuse Ly$\alpha$, continuum and H$\alpha$ emission observed around galaxies at $z\sim6$. We model the surface brightness profiles of the diffuse halos considering the fluorescent emission powered by ionizing photons escaping from the central galaxies, and the nebular emission from satellite star-forming sources, by extending the formalisms developed in Mas-Ribas & Dijkstra (2016) and Mas-Ribas et al. (2017). The comparison between our predicted profiles and Ly$\alpha$ observations at $z=5.7$ and $z=6.6$ favors a low ionizing escape fraction, $f_{\rm esc}^{\rm ion}\sim5\%$, for galaxies in the range $-19\gtrsim M_{\rm UV} \gtrsim -21.5$. However, uncertainties and possible systematics in the observations do not allow for firm conclusions. We predict H$\alpha$ and rest-frame visible continuum observations with JWST, and show that JWST will be able to detect extended (a few tens of kpc) fluorescent H$\alpha$ emission powered by ionizing photons escaping from a bright, $L\gtrsim 5L^*$, galaxy. Such observations can differentiate fluorescent emission from nebular emission by satellite sources. We discuss how observations and stacking of several objects may provide unique constraints on the escape fraction for faint galaxies and/or the abundance of ultra-faint radiation sources.

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L. Mas-Ribas, J. Hennawi, M. Dijkstra, et. al.
Wed, 26 Jul 17

Comments: 9 pages, 4 figures, re-submitted after referee report to ApJ

Dust properties of the cometary globule Barnard 207 (LDN 1489) [GA]

Barnard 207 (B207, LDN 1489, LBN 777), also known as the Vulture Head nebula, is a cometary globule in the Taurus-Auriga-Perseus molecular cloud region. B207 is known to host a Class I protostar, IRAS 04016+2610, located at a projected distance of ~8,400 au from the dense core centre. Using imaging and photometry over a wide wavelength range, from UV to sub-mm, we study the physical properties of B207 and the dust grains contained within. The core density, temperature, and mass are typical of other globules found in the Milky Way interstellar medium (ISM). The increase in the dust albedo with increasing optical wavelengths, along with the detection of coreshine in the near infrared, indicates the presence of larger dust grains in B207. The measured optical, near-, mid- and far-infrared intensities are in agreement with the CMM+AMM and CMM+AMMI dust grain type of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), suggesting mantle formation on the dust grains throughout the globule. We investigate the possibility of turbulence being responsible for diffusing dust grains from the central core to external outer layers of B207. However, in situ formation of large dust grains cannot be excluded.

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A. Togi, A. Witt and D. John
Wed, 26 Jul 17

Comments: 13 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics

Production, Processing and Consumption of the Dust in the Galaxy [SSA]

The recent results obtained by the modern telescopes and spacecrafts allow us for the first time to compare directly the mass, spatial density and size distribution of the dust grains in the regions of their production, processing and consumption in our Galaxy. The ALMA and VLT/SPHERE telescopes allow us to estimate the production of the dust by supergiants and collapsing core supernovae. The 2MASS, WISE, SDSS, Planck and other telescopes allow us to estimate the processing of the dust in the interstellar medium. After renewed Besan\c{c}on Galaxy model the medium appears to contain about half the local mass of matter (both baryonic and dark) in the Galactic neighborhood of the Sun. The Helios, Ulysses, Galileo, Cassini and New Horizons spacecrafts allow us to estimate the consumption of the dust into large solid bodies. The results are consistent each other assuming the local mean spatial density of the dust is about of $3.5\times10^{-26}$ g/cm$^3$, mean density of the grain is about 1 g/cm$^3$, and the dust production rate is about of 0.015 Solar mass per year for whole the Galaxy.

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G. Gontcharov
Wed, 26 Jul 17

Comments: 4 pages, 1 figure, conference proceedings Stars: From Collapse to Collapse, Proceedings of a conference held at Special Astrophysical Observatory, Nizhny Arkhyz, Russia 3-7 October 2016. Edited by Yu. Yu. Balega, D. O. Kudryavtsev, I. I. Romanyuk, and I. A. Yakunin. San Francisco: Astronomical Society of the Pacific, 2017, p.71

What sets the central structure of dark matter haloes? [CEA]

Dark matter (DM) haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers. While standard cold dark matter simulations readily produce haloes that follow the universal Navarro-Frenk-White (NFW) density profile with an inner slope, $\rho \propto r^{-\alpha}$, with $\alpha=1$, recent simulations have found that when the free-streaming cut-off is resolved, the resulting haloes follow nearly power-law density profiles of $\alpha\sim1.5$. In this paper, we study the formation of density cusps in haloes using idealized $N$-body simulations of the collapse of proto-haloes. When the proto-halo profile is initially cored due to particle free-streaming at high redshift, we universally find $\sim r^{-1.5}$ profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations. Quite in contrast, when the proto-halo has a power-law profile, then we obtain profiles compatible with the NFW shape when the density slope of the proto-halo patch is shallower than a critical value, $\alpha_{\rm ini} \sim 0.3$, while the final slope can be steeper for $\alpha_{\rm ini}\gtrsim 0.3$. We further demonstrate that the $r^{-1.5}$ profiles are sensitive to small scale noise, which gradually drives them towards an inner slope of $-1$, where they become resilient to such perturbations. We demonstrate that the $r^{-1.5}$ solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

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G. Ogiya and O. Hahn
Wed, 26 Jul 17

Comments: 22 pages, 20 figures, 2 tables, submitted to MNRAS, Figure 9 summarizes the main results