Day 553

Tuesday.

1311.5888
The large-scale structure of the halo of the Andromeda galaxy part I:  global stellar density, morphology and metallicity properties
Ibata et al

Analysis of the LSS of the halo of the Andromeda, based on PAndAS, currently the most complete map of the resolved stellar populations in any galactic halo.  Global halo populations hollow closely power law profiles that become steeper with increasing metallicity.  Fit a 3d halo models (divide sample into stream-like populations and smooth halo component).  The most metal-poor populations ([Fe/H]<-1.7) are distributed approximately spherically (slightly prolate with ellipticity c/a=1.09pm0.03), with only a relatively small fraction (42%) residing in discernible stream-like structures.  The sphericity of the ancient smooth component strongly hints that the DM halo is approximately spherical.  More metal-rich populations contain higher fractions of stars in stream (86% for [Fe/H]>-0.6).  The space density of the smooth metal-poor component has a global power-law slope of =3.08pm0.07, and a non-parametric fit shows that this slope remains nearly constant from 30 kpc to 300 kpc.  The total stellar mass in the halo at distances beyond 2 degrees is 1.1e10 Msun, while that of the smooth component is 3e9 Msun.  Extrapolating into the inner galaxy, the total stellar mass of the smooth halo is plausibly 8e9 Msun.  Detect a substantial metallicity gradient, which declines from [Fe/H]=-0.7 at R=30kpc to [Fe/H]=-1.5 at R=150kpc for the full sample, with the smooth halo being 0.2 dex more metal poor than the full sample at each radius.  While qualitatively in-line with expectations from cosmological simulations, these observations are of great importance as they provide a prototype template that such simulations must now be able to reproduce in quantitative detail.
1311.5893
Herschel-ATLAS: modelling the first strong gravitational lenses
Dye et al

Determine the mass-density radial profiles for the first 5 SL discovered by Herschel.  The logarithmic slope of the total mass density profile steepens with decreasing redshift; the slope is positively correlated with the average total projected mass density of the lens contained within half the effective radius and negatively correlated with the effective radius; the fraction of DM contained within half the effective radius increases with increasing effective radius and increases with redshift.

1311.5895
An improved measurement of baryon acoustic oscillations from the correlation function of galaxy clusters at z~0.3
Veropalumbo et al

Use 25k clusters from SDSS, estimate from the projected correlation function a bias of 2.06 pm 0.04.  BAO peak determined with high accuracy; s_p=108.10pm4.00 Mpc/h, in good agreement with previous estimates with similar uncertainty.

1311.5916
How galaxies become red: insights from cosmological simulations
Cen

An analysis of more than 3k galaxies resolved better than 114 pc/h at z=0.62 in a LAOZI cosmological AMR hydrosim is performed and insights gained on quenching and color migration.  The vast majority of red galaxies are found to be within 3 virial radii of a larger galaxy, at the onset of quenching.  Thus call this mechanism "environment quenching", which encompasses satellite quenching.  Two physical processes are largely responsible: ram-pressure stripping first disconnects the galaxy from the cold gas supply on large scales, followed by a longer period of cold gas starvation taking place in high velocity dispersion environment, during the early part of which the existing dense cold gas in the central region (=<10 kpc) is consumed by in situ star formation.  Quenching is found to be more efficient but not faster, on average, in denser environment.  Throughout quenching galaxies follow nearly vertical tracks in the color-stellar-mass diagram.  In contrast, individual galaxies of all masses grow most of their stellar masses in the blue cloud, prior to the onset of quenching, and progressively more massive blue galaxies with already relatively older mean stellar ages continue to enter the red sequence.  Consequently, correlations among observables of red galaxies - such as the age-mass relation - are largely inherited from their blue progenitors at the onset of quenching.  While the color makeup of the entire galaxy population strongly depends on environment, which is a direct result of environment quenching, physical properties of blue galaxies as a sub-population show little dependence on environment.  A variety of predictions from the simulation are shown to be in accord with extant observations.