The Impact of Environment on Late-time Evolution of the Stellar Mass-Halo Mass Relation

At a fixed halo mass, galaxy clusters with larger differences in brightness between the brightest central galaxy (BCG) and fourth-brightest cluster member (m _gap) have larger BCG stellar masses. Recent studies have shown that by including m _gap as a latent parameter in the cluster stellar mass-halo mass (SMHM) relation, one can make more precise measurements of the SMHM relation’s amplitude, slope, and intrinsic scatter. We use galaxy clusters from the Sloan Digital Sky Survey to measure the SMHM-m _gap relation and its evolution out to z = 0.3. Using a fixed comoving aperture of 100 kpc to define the central galaxy’s stellar mass, we report statistically significant negative evolution in the slope of the SMHM relation to z = 0.3 (>3.5σ). The steepening of the slope over the past 3.5 Gyr can be explained by late-time merger activity at the cores of galaxy clusters. We also find that the inferred slope depends on the aperture used to define the radial extent of the central galaxy. At small radii (20 kpc), the slope of the SMHM relation is shallow, indicating that the core of the central galaxy is less related to the growth of the underlying host halo. By including all of the central galaxy’s light within 100 kpc, the slope reaches an asymptote value.