ELUCID IV: Galaxy Quenching and its Relation to Halo Mass, Environment, and Assembly Bias

Huiyuan Wang, H. J. Mo, Sihan Chen, Yang Yang, Xiaohu Yang, Enci Wang, Frank C. van den Bosch, Yipeng Jing, Xi Kang, Weipeng Lin, S. H. Lim, Shuiyao Huang, Yi Lu, Shijie Li, Weiguang Cui, Youcai Zhang, Dylan Tweed, Chengliang Wei, Guoliang Li, Feng Shi

Published 2017-07-27Version 1

We examine the quenched fraction of central and satellite galaxies as a function of galaxy stellar mass, halo mass, and the matter density of their large scale environment. Matter densities are inferred from our ELUCID simulation, a constrained simulation of the local Universe, sampled by the Sloan Digital Sky Survey (SDSS), while halo masses and the distinction between centrals and satellites are taken from the SDSS galaxy group catalog. The quenched fraction for the total population increases systematically with stellar mass, halo mass, and environmental density. In agreement with previous studies, we find that the `environmental quenching efficiency', which quantifies the quenched fraction as function of environmental density, is independent of stellar mass. This independence also holds when using halo mass as the environmental parameter. And the stellar mass independence of density-based efficiency originates from the independence of halo-based efficiency. We find that centrals and satellites follow similar correlations of quenching efficiency with halo mass and stellar mass, suggesting that they have experienced similar quenching processes. When using mass density as environmental parameter, though, the environmental dependence is much stronger for satellites than for centrals, and the quenching efficiencies of the two populations reveal a significant residual dependence on stellar mass. These are predominantly determined by the fact that centrals and satellites of the same stellar mass on average live in halos of different masses. After removing these halo-mass effects, there is a weak but significant residual in the quenched fraction of central galaxies, which is eliminated when halo assembly bias is taken into account. Our results therefore indicate that halo mass is the prime environmental parameter that regulates the quenching of both centrals and satellites.