Characterizing cool, neutral gas, and ionized metals in the outskirts of low-z galaxy clusters

ABSTRACT We present the first detection of cool, neutral gas in the outskirts of low-z galaxy clusters using a statistically significant sample of 3191 z ≈ 0.2 background quasar-foreground cluster pairs by cross-matching the Hubble Spectroscopic Legacy Archive quasar catalogue with optically- and SZ-selected cluster catalogues. The median cluster mass of our sample is ≈1014.2 $\rm {\rm M}_{\odot }$ with a median impact parameter (ρcl) of ≈5 Mpc. We detect significant Lyα, marginal C iv, but no O vi absorption in the signal-to-noise ratio weighted mean stacked spectra with rest-frame equivalent widths of 0.096 ± 0.011, 0.032 ± 0.015, and 10^{13}$ cm−2) are excluded, indicate the patchy distribution of cool gas in the outskirts. We argue that the cool gas in cluster outskirts in combination arises from the circumgalactic gas stripped from cluster galaxies and to large-scale filaments feeding the clusters with cool gas.