Discovery of a cool, metal-rich gas reservoir in the outskirts of z ~ 0.5 clusters

Abstract

We built the first-ever statistically significant sample of ≈ 80, 000 background quasar -foreground cluster pairs to study the cool, metal-rich gas in the outskirts (> R 500 ) of z ≈ 0.5 clusters with a median mass of ≈ 10 14.2 M . The sample was obtained by cross-matching the SDSS cluster catalog of Wen & Han (2015) and SDSS quasar catalog of Lyke et al. (2020). The median impact parameter (ρ cl ) of the clusters from the quasar sightlines is 2.4 Mpc (median ρ cl /R 500 = 3.6). A strong Mg ii, along with marginal Fe ii, absorption is detected in the mean and median stacked spectra of the quasars with Mg ii rest-frame equivalent widths (REWs) of 0.034 ± 0.003 Å (11σ) and 0.010 ± 0.002 Å (5σ), respectively. The Mg ii REW shows a declining trend with increasing ρ cl and ρ cl /R 500 , but does not show any significant trend with mass (M 500 ) or redshift (z cl ) within the small M 500 and z cl ranges probed here. The Mg ii absorption signal and the trends persist even if we exclude the quasar-cluster pairs where the background quasars may be probing the circum-galactic medium (CGM) of clusters' member galaxies. The Mg ii (and Fe ii) absorption reported here is the first detection of its kind. It indicates the presence of a cool, metal-rich gas reservoir surrounding galaxy clusters out to several R 500 . We suggest that the metal-rich gas in the cluster outskirts arise from stripped materials and that gas stripping becomes important out to large clustocentric distances (> 3R 500 ).

Gas distribution from clusters to filaments in IllustrisTNG

“…Recently, Artale et al (2022) found that Mg II, C II, and Si IV are efficient tracers of the halo gas in dense environment, whereas Ne VIII, N V, O VI, and C IV are better tracers of warm hot and low-density gas (WHIM) inside filamentary structure at large scales (and z=0). In particular, the small fraction of halo gas phase inside clusters (with T < 10 5 K and n H > 10 −4 cm −3 ) is supposed to be condensed gas inside halos in high-density and low-temperature star-forming regions, as recently observed via Mg II absorption lines by Lee et al (2021), Anand et al (2022), andMishra &Muzahid (2022). For example, Lee et al (2021) showed that Mg II absorbers are more abundant inside clusters than outside them (> 2R 200 ).…”