The Spatial Distribution of Satellite Galaxies Selected from Redshift Space

Ingolfur Agustsson, Tereasa G. Brainerd

Published 2015-12-28Version 1

We investigate the spatial distribution of satellite galaxies that were obtained from a mock redshift survey of the first Millennium Run simulation. The satellites were identified using typical redshift space criteria and, hence, the sample includes both genuine satellites and a large number of interlopers. As expected from previous work, the 3D locations of the satellites are well-fitted by a combination of a Navarro, Frenk & White (NFW) density profile and a power law. At fixed stellar mass, the NFW scale parameter, r_s, for the satellite distribution of red hosts exceeds that for the satellite distribution of blue hosts. In both cases the dependence of r_s on host stellar mass is well-fitted by a power law. For the satellites of red hosts, r_s^{red} \propto (M_\ast / M_sun)^{0.71 \pm 0.05} while for the satellites of blue hosts, r_s^{blue} \propto (M_\ast / M_sun)^{0.48 \pm 0.07}. For hosts with stellar masses greater than 4.0E+10 M_sun, the satellite distribution around blue hosts is much more concentrated than it is around red hosts with the same stellar mass. We perform model fits to the projected (2D) locations of the satellites and find that, with the exception of the satellites of the most massive red hosts, the 2D analysis accurately recovers the values of r_s obtained from the 3D analysis. Therefore, even in the limit of a large number of interlopers, the 3D distribution can be recovered using 2D information alone. The spatial distribution of the satellites of red hosts traces that of the hosts' halos; however, the spatial distribution of the satellites of blue hosts is more concentrated that of the hosts' halos by a factor of ~2. This calls into question whether observed satellites that are selected from redshift space can be used to directly infer the concentration of the dark matter halos of massive, blue host galaxies in our universe.