Since z \sim 1 , the stellar mass density locked in low mass groups and clusters has grown by a factor of \sim 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 \sim 3 - 4 \% of the total mass of group halos with masses 10 ^ { 12.8 } < M _ { 200 } / M _ { \odot } < 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 \sigma \sim 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 \lesssim 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 .