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 10⁴² h⁻² ergs s⁻¹ and lie on the L_X-σ_v relations defined by local groups and clusters. The upper limits for the nondetections are also consistent with the local L_X-σ_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.