Discovery of an H SPAN CLASS="sml" i-rich Gas Reservoir in the Outskirts of SZ-effect-selected Clusters

We report on the detection of three strong H i absorbers originating in the outskirts (i.e., impact parameter, (1.6-4.7)r ₅₀₀) of three massive ( M _o) clusters of galaxies at redshift , in the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) spectra of three background UV-bright quasars. These clusters were discovered by the 2500 deg² South Pole Telescope Sunyaev-Zel'dovich (SZ) effect survey. All three COS spectra show a partial Lyman limit absorber with N(H i) >10^16.5 cm^-2 near the photometric redshifts () of the clusters. The compound probability of the random occurrence of all three absorbers is <0.02%, indicating that the absorbers are most likely related to the targeted clusters. We find that the outskirts of these SZ-selected clusters are remarkably rich in cool gas compared to existing observations of other clusters in the literature. The effective Doppler parameters of the Lyman series lines, obtained using a single-cloud curve-of-growth (COG) analysis, suggest a nonthermal/turbulent velocity of a few×10 km s^-1 in the absorbing gas. We emphasize the need for uniform galaxy surveys around these fields and for more UV observations of quasar-cluster pairs in general in order to improve the statistics and gain further insights into the unexplored territory of the largest collapsed cosmic structures.