Galaxy Assembly Bias in the Stellar-to-halo Mass Relation for Red Central Galaxies from SDSS

Abstract

We report evidence of galaxy assembly bias—the correlation between galaxy properties and biased secondary halo properties at fixed halo mass (M H)—in the stellar-to-halo mass relation for red central galaxies from the Sloan Digital Sky Survey. In the M H = 1011.5-1013.5 h −1 M ⊙ range, central galaxy stellar mass (M *) is correlated with the number density of galaxies within 10 h −1 Mpc (δ 10), a common proxy for halo formation time. This galaxy assembly bias signal is also present when M H, M *, and δ 10 are substituted with group luminosity, galaxy luminosity, and metrics of the large-scale density field. To associate differences in δ 10 with variations in halo formation time, we fitted a model that accounts for (1) errors in the M H measured by the J. L. Tinker group catalog and (2) the level of correlation between halo formation time and M * at fixed M H. Fitting of this model yields that (1) errors in M H are ∼0.15 dex and (2) halo formation time and M * are strongly correlated (Spearman’s rank correlation coefficient ∼0.85). At fixed M H, variations of ∼0.4 dex in M * are associated with ∼1-3 Gyr variations in halo formation time and galaxy formation time (from stellar population fitting). These results are indicative that halo properties other than M H can impact central galaxy assembly.