First Results from the SRG/eROSITA All-Sky Survey: From Stars to Cosmology

Optical Identification and Properties of Galaxy Clusters and Groups in the Western Galactic Hemisphere

18 Sept 2024, 12:10

15m

HS 1 Hörsaal/lecture hall 1 (Garching)

Oral Cluster Surveys

Speaker

Matthias Kluge (MPE)

Description

The first SRG/eROSITA All-Sky Survey (eRASS1) provides the largest intracluster medium-selected galaxy cluster and group catalog covering the western Galactic hemisphere. Compared to samples selected purely on X-ray extent, the sample purity can be enhanced by identifying cluster candidates using optical and near-infrared data from the DESI Legacy Imaging Surveys. Using the red-sequence-based cluster finder eROMaPPer, we measured individual photometric properties (redshift $z_\lambda$, richness $\lambda$, optical center, and BCG position) for 12 000 eRASS1 clusters over a sky area of 13 116 deg$^2$, augmented by 247 cases identified by matching the candidates with known clusters from the literature. The median redshift of the identified eRASS1 sample is $z=0.31$, with 10% of the clusters at $z>0.72$. The photometric redshifts have an accuracy of $\delta z/(1+z)\lesssim0.005$ for $0.050.05$. For these and further quality assessments of the eRASS1 identified catalog, we applied our identification method to a collection of galaxy cluster catalogs in the literature, as well as blindly on the full Legacy Surveys covering 24 069 deg$^2$. Using a combination of these cluster samples, we investigated the velocity dispersion-richness relation, finding that it scales with richness as $\log(\lambda_{\rm norm})=2.401\times\log(\sigma)-5.074$ with an intrinsic scatter of $\delta_{\rm in}=0.10\pm0.01$ dex. The primary product of our work is the identified eRASS1 cluster catalog with high purity and a well-defined X-ray selection process, opening the path for precise cosmological analyses presented in companion papers.