Evidence for galaxy assembly bias in BOSS CMASS redshift-space galaxy
  correlation function
  Building accurate and flexible galaxy-halo connection models is crucial in
modeling galaxy clustering on non-linear scales. Recent studies have found that
halo concentration by itself cannot capture the full galaxy assembly bias
effect and that the local environment of the halo can be an excellent indicator
of galaxy assembly bias. In this paper, we propose an extended halo occupation
distribution model (HOD) that includes both a concentration-based assembly bias
term and an environment-based assembly bias term. We use this model to achieve
a good fit (chi^2/DoF = 1.35) on the 2D redshift-space 2-point correlation
function (2PCF) of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS
galaxy sample. We find that the inclusion of both assembly bias terms is
strongly favored by the data and the standard 5-parameter HOD is strongly
rejected. More interestingly, the redshift-space 2PCF drives the assembly bias
parameters in a way that preferentially assigns galaxies to lower mass halos.
This results in galaxy-galaxy lensing predictions that are within 1sigma
agreement with the observation, alleviating the perceived tension between
galaxy clustering and lensing. We also showcase a consistent 3-5sigma
preference for a positive environment-based assembly bias that persists over
variations in the fit. We speculate that the environmental dependence might be
driven by underlying processes such as mergers and feedback, but might also be
indicative of a larger halo boundaries such as the splashback radius.
Regardless, this work highlights the importance of building flexible
galaxy-halo connection models and demonstrates the extra constraining power of
the redshift-space 2PCF.
