On the Constraints of Galaxy Assembly Bias in Velocity Space

Abstract

If the formation of central galaxies in dark matter haloes traces the assembly history of their host haloes, in haloes of fixed mass, central galaxy clustering may show dependence on properties indicating their formation history. Such a galaxy assembly bias effect has been investigated by Lin et al. (2016), with samples of central galaxies constructed in haloes of similar mass and with mean halo mass verified by galaxy lensing measurements, and no significant evidence of assembly bias is found from the analysis of the projected two-point correlation functions of early-and late-forming central galaxies. In this work, we extend the the investigation of assembly bias effect from real space to redshift (velocity) space, with an extended construction of early-and late-forming galaxies. We carry out halo occupation distribution modelling to constrain the galaxy-halo connection to see whether there is any sign of the effect of assembly bias. We find largely consistent host halo mass for early-and late-forming central galaxies, corroborated by lensing measurements. The central velocity bias parameters, which are supposed to characterise the mutual relaxation between central galaxies and their host haloes, are inferred to overlap between early-and lateforming central galaxies. However, we find a large amplitude of velocity bias for early-forming central galaxies (e.g. with central galaxies moving at more than 50% that of dark matter velocity dispersion inside host haloes), which may signal an assembly bias effect. A large sample with two-point correlation functions and other clustering measurements and improved modelling will help reach a conclusive result.

Modeling Strong Lenses from Wide-Field Ground-Based Observations in KiDS and GAMA

“…At high masses typical of lensing elliptical galaxies, inefficiency in the stellar occupancy of dark matter haloes is ascribed to the effects of AGNs (Somerville et al 2015). Weak lensing studies (Velander et al 2014;Mandelbaum et al 2013;Lin et al 2016) and velocity field studies (McCarthy et al 2021;Posti & Fall 2021) appear to show the effects of assembly bias on the scales of galaxy populations (Cui et al 2021); assembly bias is especially noticeable at ∼ 1Mpc scales (Hearin et al 2016): i.e. groups of galaxies.…”