SLAC, Kavli 3rd Floor Conf. Room
The Stellar Mass-Halo Mass (SMHM) relation provides insight into the galaxy-dark matter halo connection. In Golden-Marx & Miller (2018), we incorporate the magnitude gap, the difference in brightness between the BCG and 4th brightest cluster member within 0.5 R200, into the cluster SMHM relation. We observe that at fixed halo mass, clusters with larger magnitude gaps have larger central galaxy stellar masses. We also see this in semi-analytic simulations, which suggests that it can be explained by the hierarchical growth of central galaxies. Accounting for the magnitude gap significantly reduces the inferred intrinsic scatter to below 0.1 dex, thus strictly limiting the model space that can explain the stellar mass growth in centrals of massive halos. Hierarchical growth also predicts that the central’s stellar mass and magnitude gap decrease with increasing lookback time. However, the extent of the growth of the central’s stellar mass is dependent upon the aperture defined by the radial extent of the central galaxy. We investigate the impact of aperture size on the slope of the SMHM relation and find that the slope is significantly steeper at larger aperture radii (~100 kpc). Using this result, we test the prediction of hierarchical growth, and present our latest results using SDSS-redMaPPer. Unlike prior studies we detect redshift evolution in the slope of the SMHM relation (measured at 100kpc aperture), which can be explained by recent merger activity.