Day 1253

Monday.

1705.01988
Revisiting HOD model assumptions: the impact of AGN feedback and assembly bias
McCullagh, Norberg, Cole, Gonzalez-Perez, Baugh, Helly

The standard HOD models were originally developed based on results from semi-analytic and hydrodynamical galaxy formation models.  Those models have since progressed, in particular to include AGN feedback to match the galaxy luminosity function in a universe with the observed baryon fraction.  AGN feedback affects the relationship between galaxy stellar mass and luminosity, in particular making the relationship non-monotonic.  For matched number density samples, galaxies in luminosity-threshed samples occupy a different range of halo masses from those in stellar-mass-threshold samples.  Find that the shapes of the HODs of luminosity-threshold samples are slightly more complicated in semi-analytic galaxy formation models that include AGN feedback than are assumed by standard HOD models.  Also find that sub halo abundance matching (SHAM) does not preserve these non-standard shapes.  Show that catalogues created using SHAM and the semi-analytic model Galform that have the same large-scale 2-pt clustering by construction have different void probability functions (VPFs) in both real and redshift space.  Find that these differences arise from the different HOD shapes, as opposed to assembly bias, which indicates that the VPF could be used to test the suitability of an HOD model with real data.


1705.02071
Properties and origin of galaxy velocity bias in the Illustris simulation
Ye, Guo, Zheng, Zehavi

Use the hydrodynamical galaxy formation simulations from the ILlustris suite to study the origin and properties of galaxy velocity bias, i.e., the difference between the velocity distributions of galaxies and dark matter inside halos.  Find that galaxy velocity bias is a decreasing function of the ratio of galaxy stellar mass to host halo mass.  In general, central galaxies are not at rest with respect to dark matter halos or the core of halos, with a velocity dispersion above 0.04 times that of the DM.  The central galaxy velocity bias is found to be mostly caused by the close interactions between the central and satellite galaxies.  For satellite galaxies, the velocity bias is related to their dynamical and tidal evolution history after being accreted onto the host halos.  It depends on the time after the accretion and their distances from the halo centers, with massive satellites generally moving more slowly than the dark matter.  The results are in broad agreements with those inferred from modeling small-scale redshift-space galaxy clustering data, and the study can help improve models of z-space galaxy clustering.