X-Ray Studies of the Abell 3158 Galaxy Cluster with eROSITA

Abstract

Context. The most nearby clusters are the best places to study physical and enrichment effects in the faint cluster outskirts. The Abell 3158 cluster (A3158), located at z = 0.059 is quite extended with a characteristic radius r 200 = 23.95 arcmin. The metal distribution in the outskirts of this cluster has previously been studied with XMM-Newton. In 2019, A3158 was observed as a calibration target in a pointed observation with the eROSITA telescope onboard the Spektrum-Roentgen-Gamma (SRG) mission. Bright large clusters, like A3158, are ideal for studying the metal distribution in the cluster outskirts, along with the temperature profile and morphology. With the deeper observation time of the eROSITA telescope, these properties can be studied in greater detail and at larger radii now. Furthermore, bright nearby clusters are ideal X-ray instrumental cross-calibration targets as they cover a large fraction of the detector and do not vary in time.Aims. We first aim to compare the temperature, metal abundance and normalisation profiles of the cluster from eROSITA with previous XMM-Newton and Chandra data. Following this calibration work, we aim to investigate the temperature and metallicity of the cluster out to close to r 200 , measure the galaxy velocity dispersion, and determine the cluster mass. Furthermore, we aim to search for infalling clumps and background clusters in the field. Methods. We determined 1d temperature, abundance and normalisation profiles from both eROSITA and XMM-Newton data as well as 2d maps of temperature and metal abundance distribution from eROSITA data. The velocity dispersion was determined and the cluster mass was calculated from the mass -velocity dispersion (M 200 -σ v ) relation. Galaxy density maps were created to get a better understanding of the structure of the cluster and the outskirts. Results. The overall (i.e., in the range 0.2 − 0.5r 500 ) temperature was measured to be 4.725 ± 0.035 keV. The temperature, abundance and normalisation profiles of eROSITA all agree on a 10% level with those we determined using XMM-Newton and Chandra data; and they are also consistent with the profiles published previously by the X-COP project. The Abell 3158 cluster morphology and surface brightness profile look regular at a first glance. Clusters that have such profiles typically are relaxed and host cool cores. However, from the temperature profile and map we see that the cluster lacks a cool core, as was noted before. Instead, the presence of an off-centre cool clump to the west of the central cluster region, which has been previously detected, is observed. These are indications that the cluster may be undergoing some sloshing and merger activity. Furthermore there is a bow shaped edge near the location of the cool gas clump West of the cluster centre. Further out in the West of the X-ray images of A3158 an extension of gas is detected; the larger scale extension described here for the first time. The velocity dispersion of the cluster member galaxies was measured to be 1058 ± 41km s −1 ba...

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