Observation of a Very Massive Galaxy Cluster at = 0.76 in the SRG/eROSITA All-Sky Survey

The results of multiwavelength observations of the very massive galaxy cluster SRGe CL2305.2–2248 detected in X-rays during the first SRG/eROSITA all-sky survey are discussed. This galaxy cluster has also been detected previously in the millimeter band in the South Pole Telescope (SPT-CL J2305–2248) and Atacama Cosmology Telescope (ACT-CL J2305.1–2248) surveys through the observation of the Sunyaev–Zeldovich effect. The spectroscopic redshift has been measured at the 6-m BTA telescope, . In addition, deep photometric measurements of galaxies have been performed at the Russian–Turkish 1.5-m telescope (RTT-150). The mass of the cluster is estimated from the eROSITA data to be . We show that this cluster is among several tens of the most massive clusters in the observable Universe and among only a few most massive galaxy clusters at .