Day 664

Saturday, Sunday.

1401.7328
From voids to Coma: the prevalence of pre-processing in the local Universe
Cybulski et al

Quantify the degree to which SF activity is quenched as a function of environment: examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over 500 sq deg.  Vornoi Tesselation to characterize density field, and Minimal Spanning Tree to define continuous structures.  Environment = cluster, group, filament, and void; quantify the degree to which environment contributes to quenching of SF activity.  Sample covers over two orders of magnitude in stellar mass (1e8.5 to 11 Msun), and consequently trace the effects of environment on SF activity for dwarf and massive galaxies, distinguishing so-called "mass quenching" from "environment quenching".  Environmentally-driven quenching of SF activity, measured relative to the void galaxies, occurs to progressively greater degrees in filaments, groups, and clusters, and this trend holds for dwarf and massive galaxies alike.  A similar trend is found using g-r colors, but with a more significant disparity between galaxy mass bins driven by increased internal dust extinction in massive galaxies.  The SFR distributions of massive SF galaxies have no significant environmental dependence, but the distributions for dwarf SF galaxies are found to be statistically distinct in most environments.  Pre-processing plays a significant role at low redshift, as environmentally-driven galaxy evolution affects nearly half of the galaxies in the group environment, and a significant fraction of the galaxies in the more diffuse filaments.  Study underscores the need for sensitivity to dwarf galaxies to separate mass-driven from environmentally-driven effects, and the use of unbiased tracers of SF activity.

1401.7329
Stellar mass -- halo mass relation and star formation efficiency in high-mass halos
Kravtsov, Vikhlinin, Meschscheryakov

Compare stellar and halo mass: M* from optical and IR data, and total mass from X-ray observations.  Find that stellar mass of BCGs scales as M500^a_BCG with a_BCG~0.35pm0.1 and scatter of M*BCG at a fixed M500 of ~0.2 dex.  Show that M*-M relations from abundance matching or halo modeling reported in recent studies underestimate stellar masses of BCGs by a factor of ~2-4, because these studies used stellar mass functions based on photometry that severely underestimates the outer surface brightness profiles of massive galaxies.  Show that M*-M relation derived using abundance matching with the recent SMF calibration by Bernardi+2013 based on improved photometry is in a much better agreement with the relation with the derived relation here.  The total stellar mass of galaxies correlates with total mass M500 with the slope of approximately 0.6pm0.1 and scatter of 0.1 dex.  This indicates that efficiency with which baryons are converted into stars decreases with increasing cluster mass. Show that for a fixed choice of the IMF the total stellar fraction in clusters is only a factor of ~3-5 lower than the peak stellar fraction reached in M~1e12 Msun halos, and only a factor of ~1.5-3 if the IMF becomes progressively more bottom heavy with increasing mass in early type galaxies, as indicated by recent observations. The larger normalization and slope of the M*-M relation derived in this study shows that the overall efficiency of SF in massive haloes is suppressed much less than was thought before and that feedback and associated suppression of SF in massive haloes should be weaker than assumed in most of the current SAM and simulations.  

1407.7331
Galaxy and mass assembly (GAMA): fine filaments of galaxies detected within voids
Alpaslan, et al

Based on GAMA, report discovery of structures that are 'tendrils' of galaxies: coherent, thin chains of galaxies that are rooted in filaments and terminate in neighboring filaments or voids. On average, tendrils contain 6 galaxies and span 10 Mpc/h.  Use the so-called line correlation function to prove that tendrils represent real structures rather than accidental alignments.  Show that voids found in DR7 survey that overlap with GAMA contain a large number of galaxies, primarily belonging to tendrils.  This implies that void sizes are strongly dependent on the number density and sensitivity limits of a survey.  Caution that galaxies in low density regions, that may be defined as 'void galaxies', will have local galaxy number densities that depend on such observational limits and are likely higher than can be directly measured.

1401.7657
Analytical model for non-thermal pressure in galaxy clusters
Shi, Komatsu

Non-thermal pressure in the intracluster gas has been found ubiquitously in numerical simulations, and observed indirectly.  In this paper, develop an analytical model for intracluster non-thermal pressure.  Write down and solve a first-order differential equation describing the evolution of non-thermal velocity dispersion.  This equation is based on insights gained from observations, numerical simulations, and theory of turbulence.  The non-thermal energy is sourced, in a self-similar fashion, by the mass growth of clusters via mergers and accretion, and dissipates with a time scale determined by the turnover time of the largest turbulence eddies.  Model predicts a radial profile of non-thermal pressure for relaxed clusters.  The non-thermal fraction increases with radius, redshift, and cluster mass, in agreement with numerical simulations.  The radial dependence is due to a rapid increase of the dissipation time scale with radii, and the mass and redshift dependence comes from the mass growth history.  Combining model for the non-thermal fraction with the Komatsu-Seljak model for the total pressure, obtain thermal and non-thermal pressure profiles, and compute the hydrostatic mass bias.  Find typically 10% bias for the hydrostatic mass enclosed within r500.

1401.7669
A panchromatic analysis of starburst galaxy M82: probing the dust properties
Hutton et al

Combine NUV, optical and IR imaging of M82 to explore the properties of dust both in the ISM of the galaxy and the dust entrained in the superwind.  The three NUV filters of Swift/UVOT enable detail probing of the properties of the extinction curve in the region around the 2175A bump.  The NUV color-color diagram strongly rules out a Calzetti-type law, which can either reflect intrinsic changes in the dust properties or in the SFH compared to starbursts well represented by such an attenuation law.  Emphasize that it is mainly in the NUV region where a standard MW-type law is preferred over a Calzetti law.  The age and dust distribution of the stellar populations is consistent with the scenario of an encounter with M81 in the recent 400 Myr.  The radial gradients of the NUV and optical colors in the super wind region support the hypothesis that the emission in the wind cone is driven by scattering from dust grains entrained in the ejecta.  The observed wavelength dependence reveals either a grain size distribution $n(a)\propto a^-2.5, where a is the size of the grain, or a flatter distribution with a maximum size cutoff, suggesting that only small grains are entrained in the SNe-driven wind.

1401.7878
A new method for classifying galaxy SEDs from multi-wavelength photometry
Wild et al

From optical-NIR SEDs of galaxies, a new method to classify them using 3 shape parameters (super-colors) based on PCA of model SEDs.  As well as cleanly separating a tight red-sequence from star-forming galaxies, 3 unusual populations are identifiable by their unique colors: very dusty SF galaxies with high metallicity and old mean stellar age; post-starburst galaxies which have formed greater than around 10% of their mass in a recent unsustained SB event; and metal-poor quiescent dwarf galaxies.  Find that quiescent galaxies account for 45% of galaxies with log(M*/Msun)>11, declining steadily to 13% at log (M*/Msun)=10.  The properties and mass-function of the post-starburst galaxies are consistent with a scenario in which gas-rich mergers contribute to the growth of the low and intermediate mass range of the red sequence.