Galaxy cluster virial-shock sources in eROSITA catalogs

Context. Virial shocks around galaxy clusters and groups are being mapped, thus tracing accretion onto large-scale structure. Aims. 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 deg2 field. Methods. 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. Results. We find an excess of X-ray sources narrowly localized at the 2:0 < r=R500 < 2:25 normalized radii, just inside the anticipated virial shocks, of the resolved 532 clusters, for samples of both extended sources (3s for 534 sources) and bright sources (3:5s for 5820 sources; 4s excluding the low cluster-mass quartile). The excess sources are on average extended (∼100 kpc), luminous (LX ' 1043-44 erg s-1), 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 LX expected at EDR redshifts and a possible dependence on host mass. Conclusions. Localized virial-shock spikes in the distributions of discrete radio, X-ray, and possibly also ?-ray 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.