eRASS. Optical properties of clusters and groups

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 measure individual photometric properties (redshift z_lambda richness lambda, optical center, and BCG position) for 12000 eRASS1 clusters over a sky area of 13116deg^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)<0.005 for 0.05<z<0.9. Spectroscopic cluster properties (redshift z_spec and velocity dispersion sigma) are measured a posteriori for a subsample of 3210 and 1499 eRASS1 clusters, respectively, using an extensive compilation of spectroscopic redshifts of galaxies from the literature.