Letter to the Editor

Galaxy cluster virial-shock sources in eROSITA catalogs

Physics Department, Ben-Gurion University of the Negev, PO Box 653 Be’er-Sheva 84105, Israel
e-mail: keshet.uri@gmail.com

Received: 29 February 2024
Accepted: 11 April 2024

Abstract

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 (3σ for 534 sources) and bright sources (3.5σ for 5820 sources; 4σ excluding the low cluster-mass quartile). The excess sources are on average extended (∼100 kpc), luminous (L_X ≃ 10^{43 − 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 L_X 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 γ-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.