Galaxy cluster virial-shock sources in eROSITA catalogs

Abstract

Virial shocks around galaxy clusters and groups are being mapped, thus tracing accretion onto large-scale structure. Following the recent identification of discrete ROSAT and radio sources associated with the virial shocks of MCXC clusters and groups, we examined the eROSITA-DE Early Data Release (EDR) to see whether it shows virial-shock X-ray sources within its $140$ deg$^2$ field. EDR catalog sources were stacked and radially binned around EDR catalog clusters and groups. The properties of the excess virial-shock sources were inferred statistically by comparing the virial-shock region to the field. We find an excess of X-ray sources narrowly localized at the $2.0<r/R_ <2.25$ normalized radii, just inside the anticipated virial shocks, of the resolved 532 clusters, for samples of both extended sources ($3 for 534 sources) and bright sources ($3.5 for 5820 sources; $4 excluding the low cluster-mass quartile). The excess sources are on average extended ($ luminous ($L_X scriptsize-- $ erg s$^ $), and hot (keV scales), consistent with infalling gaseous halos crossing the virial shock. The results agree with the stacked ROSAT--MCXC signal, showing the higher $L_X$ expected at EDR redshifts and a possible dependence on host mass. Localized virial-shock spikes in the distributions of discrete radio, X-ray, and possibly also sources are new powerful probes of accretion from the cosmic web.\ We expect that data from future all-sky catalogs will allow us to place strong constraints on virial shock physics.