The Stellar Mass - Halo Mass Relation for Low Mass X-ray Groups at
  0.5<z<1 in the CDFS with CSI
  Since z~1, the stellar mass density locked in low mass groups and clusters
has grown by a factor of ~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 (CDFS). 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 ~3-4% of the total mass of
group halos with masses 10^{12.8}<M200/Msun<10^{13.5} (about the mass of Fornax
and 1/50th 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
~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<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.
