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 (SHMR) for red central galaxies from the Sloan Digital Sky Survey. In the M${}_H=10^{11.5}-10^{13.5}{h}^{-1}$ M${}_{\odot }$ range, central galaxy stellar mass (M${}_{\ast }$) is correlated with the number density of galaxies within $10h^{-1}$ Mpc ($\hat{I}{´}_{10}$), a common proxy for halo formation time. This galaxy assembly bias signal is also present when M${}_H$, M${}_{\ast }$, and $\hat{I}{´}_{10}$ are substituted with group luminosity, galaxy luminosity, and metrics of the large-scale density field. To associate differences in $\hat{I}{´}_{10}$ with variations in halo formation time, we fitted a model that accounts for (1) errors in the M${}_H$ measured by the Tinker 2021, 2022 group catalog and (2) the level of correlation between halo formation time and M${}_{\ast }$ 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${}_{\ast }$ are strongly correlated (Spearman's rank correlation coefficient ~0.85). At fixed M${}_H$, variations of ~0.4 dex in M${}_{\ast }$ are associated with ~1-3 Gyr variations in halo formation time and in galaxy formation time (from stellar population fitting; Oyarzún et al. 2022). These results are indicative that halo properties other than M${}_H$ can impact central galaxy assembly.

Accepted for publication in ApJ. 11 pages and 6 figures