Constraints on Assembly Bias from Galaxy Clustering

TL;DR

This paper constrains galaxy assembly bias using SDSS data and a decorated HOD model, revealing significant assembly bias effects in certain galaxy samples and emphasizing its importance in galaxy clustering analyses.

Contribution

It introduces the first constraints on HOD models that include assembly bias, demonstrating its significance in galaxy clustering and improving analysis methods.

Findings

Galaxy assembly bias cannot be ruled out with clustering data alone.

Strong central galaxy assembly bias is favored in certain luminosity samples.

Satellite galaxy assembly bias is significant for the faintest galaxy sample.

Abstract

We constrain the newly-introduced decorated Halo Occupation Distribution (HOD) model using SDSS DR7 measurements of projected galaxy clustering or r-band luminosity threshold samples. The decorated HOD is a model for the galaxy-halo connection that augments the HOD by allowing for the possibility of galaxy assembly bias: galaxy luminosity may be correlated with dark matter halo properties besides mass, Mvir. We demonstrate that it is not possible to rule out galaxy assembly bias using DR7 measurements of galaxy clustering alone. Moreover, galaxy samples with Mr < -20 and Mr < -20.5 favor strong central galaxy assembly bias. These samples prefer scenarios in which high-concentration are more likely to host a central galaxy relative to low-concentration halos of the same mass. We exclude zero assembly bias with high significance for these samples. Satellite galaxy assembly bias is significant for the faintest sample, Mr < -19. We find no evidence for assembly bias in the Mr < -21 sample. Assembly bias should be accounted for in galaxy clustering analyses or attempts to exploit galaxy clustering to constrain cosmology. In addition to presenting the first constraints on HOD models that accommodate assembly bias, our analysis includes several improvements over previous analyses of these data. Therefore, our inferences supersede previously-published results even in the case of a standard HOD analysis.