Day 589

Friday.  Saturday.
1402.2976
On the universality of void density profiles
Riccardelli, Quilis, Varela

Show: void density profile is insensitive to the void radius both in a catalogue of observed voids and in voids from a large cosmological simulation.  However, the observed and simulated voids display different profile shapes, with the former having much steeper profiles than the latter.  Sparsity canon be the main reason for this discrepancy.  The observed profile shows a significant dependence on the galaxy sample used to trace the matter distribution.  Samples including low-mass galaxies lead to shallower profiles wrt the samples where only massive galaxies are used, as faint galaxies live closer to the void center.  Argue that galaxies are biased tracers when used to probe the matter distribution within voids.

1402.3267
The 400d galaxy cluster survey weak lensing programme: III: evidence for consistent WL and X-ray masses at $z\approx 0.5$
Israel, Reiprich, Erben, Massey, Sarazin, Schneider, Vikhlinin

Extend calibration of WL-X-ray mass scaling down to 1e14 Msun in a sample representative of z~0.4-0.5 population, in 8 clusters (0.39<z<0.80).  Overall find good agreement between WL and X-ray masses, with different mass bias estimators consistent with zero.  Subdividing the sample, find the high-mass subsample to show no significant mass bias while for the low-mass subsample, there is a bias towards overestimated X-ray masses at the ~2sigma level for some mass proxies.  Overall scatter in the relation is low.  Do not find evidence for a strong (~40%) underestimate in the X-ray masses, as suggested to reconcile PLanck cluster counts and cosmological constraints.  For high-mass clusters, measurements are consistent with studies in the literature.  The mass dependent bias, significant at ~2sigma, may hit at a physically different cluster population (less relaxed clusters with more substructure and mergers); or it may be due to small number statistics.

1402.0003
The progenitors of local ultra-massive galaxies across cosmic time: from dusty star-bursting to quiescent stellar populations
Marchesini, Muzzin, … et al

Using the UltraVISTA catalogs, investigate the evolution in the 11.4 Gyr since z=3 of the progenitors of local ultra-massive galaxies log(M*/Msun)~11.8 (UMGs), providing a complete and consistent picture of how the most massive galaxies at z=0 have assembled.  Select progenitors with a SAM approach using abundance matching; infer growth in stellar mass of 0.56 / 0.45 / 0.27 dex from z=3/2/1, respectively, to z=0. At z<1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations.  At z>1, the contribution from SF galaxies progressively increases, with the progenitors at 2<z<3 being dominated by massive (M*~2e11 Msun), dusty (A_V~1-2.2 mag), SF (SFR~100-400 Msun/yr) galaxies with a large range in stellar ages.  At z=2.75, ~15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color.  Findings indicate that local UMGs have been mostly assembled between z=3 and z=1.5.  Most of the quenching of the SF progenitors happened between z=2.75 and z=1.25, in good agreement with the typical formation redshift and scatter in age of z=0 UMGs as derived from their fossil records.  Show that the progenitors of local UMGs, including the SF ones, have never lived on the blue cloud since z=3, challenging previously proposed pictures for the formation of local massive spheroids; propose an alternative path for the formation of local UMGs consistent with findings.

1402.0006
The total infrared luminosity may significantly overestimate the star formation rate of recently quenched galaxies
Hayward et al

The total IR luminosity is very useful for estimating the SFR of galaxies, but converting the IR luminosity into an SFR relies on assumptions that do not hold for all galaxies.  Test the effectiveness of the IR luminosity as an SFR indicator by applying it to synthetic SEDs generated from 3d hydro-sims of isolated disk galaxies and galaxy mergers.  In general, the SFR inferred from the IR luminosity agrees well with the true instantaneous SFR of the simulated galaxies.  However, for the major mergers in which a strong starburst is induced, the SFR inferred from the IR luminosity can overestimate the instantaneous SFR during the post-starburst phase by greater than two orders of magnitude.  Even though the instantaneous SFR decreases rapidly after the starburst, the stars that were formed in the starburst remain dust-obscured and thus produce significant IR luminosity.  Consequently, use of the IR luminosity as an SFR indicator may cause one to conclude that post-starburst galaxies are still star-forming, whereas in reality, SF was recently quenched.

1402.0021
Kinematic structure of massive star-forming regions - I. Accretion along filaments
Trackenberg et al

MIR and FIR view on high-mass star formation has shed light on many aspects of massive SF, but these continuum studies lack kinematic information.  Study the kinematics of the molecular gas in high-mass SF regions.  Complement PACS and SPIRE FIR data on 16 high-mass SF regions from the Herschel key project EPoS with N2H+ molecular line data from the MOPRA and Nobeyama 45m telescope.  Using the full N2H+ hyperfine structure, produce column density, velocity, and line width maps.  These were correlated with PACS 70 um images and PACS point sources.  Additionally searched for velocity gradients.  For several regions, the data suggest that the line width on the scale of clumps is dominated by outflows or unresolved velocity gradients.  2 objects show two velocity components along several LoS.  Find that all regions with a diameter larger than 1pc show either velocity gradients or fragment into independent structures with distinct velocities.  The velocity profiles of 3 regions with a smooth gradient are consistent with gas flows along the filament, suggesting accretion flows onto the densest regions.  Show that the kinematics of several regions have a significant and complex velocity structure.  For 3 filaments, suggest that gas flows toward the more massive clumps are present.