The Stellar Mass - Halo Mass Relation for Low Mass X-ray Groups at 0.5<z<1 in the CDFS with CSI

Since z similar to 1, the stellar mass density locked in low-mass groups and clusters has grown by a factor of similar to 8. Here, we make the first statistical measurements of the stellar mass content of low-mass X-ray groups at 0.5 < z < 1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and infrared surveys. Groups are selected from combined Chandra and XMM-Newton X-ray observations in the Chandra Deep Field South. These ultra-deep observations allow us to identify bona fide low-mass groups at high redshift and enable measurements of their total halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise similar to 3%-4% of the total mass of group halos with masses 10(12.8) < M-200/M-circle dot < 10(13.5) (about the mass of Fornax and one-fiftieth the mass of Virgo). Complementing our sample with higher mass halos at these redshifts, we find that the stellar-to-halo mass ratio decreases toward higher halo masses, consistent with other work in the local and high redshift universe. The observed scatter about the stellar-halo mass relation is sigma similar to 0.25 dex, which is relatively small and suggests that total group stellar mass can serve as a rough proxy for halo mass. We find no evidence for any significant evolution in the stellar-halo mass relation since z less than or similar to 1. Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly leads to such halos growing in number density and hosting increasing shares of quiescent galaxies.