The X-ray Properties of Moderate-redshift Galaxy Groups Selected by Association with Gravitational Lenses

We present results from a systematic investigation of the X-ray properties of a sample of moderate redshift (0.3<z<0.6) galaxy groups. These groups were selected not by traditional X-ray or optical search methods, but rather by an association, either physical or along the line of sight, with a strong gravitational lens. We calculate the properties of seven galaxy groups in the fields of six lens systems. Diffuse X-ray emission from the intragroup medium is detected in four of the groups. All of the detected groups have X-ray luminosities greater than 10^{42} h^{-2} erg/s, and lie on the L_X-sigma_v relations defined by local groups and clusters. The upper limits for the non-detections are also consistent with the local L_X-sigma_v relationships. Although the sample size is small and deeper optical and X-ray data are needed, these results suggest that lens-selected groups are similar to X-ray selected samples and, thus, are more massive than the typical poor-group environments of local galaxies.
Comment: Accepted for publication in ApJ (July 10, 2008 issue). New smoothing technique reveals that one system (B2108) has a multiple-peak brightness distribution. Changed discussion and figures accordingly. Corrected some values in Table 2