Constraints on Cool Gas in Rich Clusters of Galaxies

Abstract

Cool gas should be present in galaxy clusters due to stripping of galactic gas, in-fall onto the cluster, and from cooling flows. We have searched for this gas through metal resonance absorption lines from low-ionization gas toward six background quasars. Both cooling-flow and non-cooling-flow clusters were observed, with lines of sight ranging from the inner to outer parts of the cluster (0.32Mpc<=r_proj<=1.40Mpc). The HST Faint Object Spectrograph observations 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<=10¹²-10¹³ cm^-2. From existing X-ray data, we estimate that ram-pressure stripping of galactic gas by the intracluster medium should produce cool gas along these sight lines. The failure to detect absorption lines implies that any gas stripped in such a way has a low covering fraction, possibly due to a short lifetime in this low-ionization state.