Observation of a very massive galaxy cluster at z=0.76 in SRG/eROSITA all-sky survey

TL;DR

This paper reports the discovery and detailed multiwavelength analysis of a very massive galaxy cluster at redshift 0.76, combining X-ray, microwave, and optical data to estimate its mass and significance in the universe.

Contribution

It presents the first detailed multiwavelength characterization of a very massive galaxy cluster at z=0.76 detected in the SRG/eROSITA survey, including mass estimation and comparison with other massive clusters.

Findings

Cluster mass estimated as (9.0 ± 2.6) x 10^14 solar masses.

Cluster is among the few most massive at z > 0.6.

Multiwavelength data confirms the cluster's high mass and distance.

Abstract

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 was also detected earlier in microwave band through the observations of Sunyaev-Zeldovich effect in South Pole Telescope (SPT-CL J2305-2248), and in Atacama Cosmological Telescope (ACT-CL J2305.1-2248) surveys. Spectroscopic redshift measurement, $z=0.7573$, was measured at the Russian 6-m BTA telescope of SAO RAS, in good agreement with its photometric estimates, including a very accurate one obtained using machine learning methods. In addition, deep photometric measurements were made at the Russian-Turkish 1.5-m telescope (RTT150), which allows to study cluster galaxies red sequence and projected galaxies distribution. Joint analysis of the data from X-ray and microwave observations show that this cluster can be identified as a very massive and distant one using the measurements of its X-ray flux and integral comptonization parameter only. The mass of the cluster estimated according to the eROSITA data is $M_{500}=(9.0\pm2.6)\cdot10^{14}\, M_\odot$. We show that this cluster is found among of only several dozen of the most massive clusters in the observable Universe and among of only a few the most massive clusters of galaxies at $z>0.6$.