On the Constraints of Galaxy Assembly Bias in Velocity Space
  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 late-forming 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.
