Constraints on Cool Gas in Rich Clusters of Galaxies

Cool gas should be present in galaxy clusters due to stripping of galactic gas, infall onto the cluster, and from cooling flows. We searched for this gas through resonance absorption line observations from lowionization metal line gas toward six background quasars. Both cooling flow and non-cooling flow clusters were observed, with lines of sight from the inner to outer parts of the cluster (0.2 ≤ rproj/Rcluster ≤ 0.7). The HST/FOS spectra failed to detect Fe II or Mg II absorption at the cluster redshift, with 1-σ upper limits on the ion column densities of N ≤ 10–10 cm. The failure to detect absorption lines implies that the cool cluster gas either is more highly ionized or it has a low covering factor.