Optical Identification of Galaxy Clusters among SRG/eROSITA X-ray Sources Based on Photometric Redshift Estimates for Galaxies

We discuss an algorithm whereby the massive galaxy clusters detected in the SRG/eROSITA all-sky survey are identified and their photometric redshifts are estimated. For this purpose, we use photometric redshift estimates for galaxies and WISE forced photometry. To estimate the algorithm operation quality, we used a sample of 634 massive galaxy clusters from the Planck survey with known spectroscopic redshifts in the range $0.1 < z_{spec} < 0.6$. The accuracy of the photometric redshift estimates for this sample is $δz_{phot}/(1+z_{phot}) \approx 0.5$%, the fraction of large deviations is 1.3%. We show that these large deviations arise mainly from the projections of galaxy clusters or other large-scale structures at different redshifts in the X-ray source field. Measuring the infrared (IR) luminosities of galaxy clusters allows one to estimate the reliability of the optical identification of the clusters detected in the SRG/eROSITA survey and to obtain an additional independent measurement of their total gravitational masses, $M_{500}$. We show that the masses $M_{500}$ of the galaxy clusters estimated from their IR luminosity measurements have an accuracy $σ_{\lg\,M_{500}} = 0.124$, comparable to the accuracy of the mass estimation for the galaxy clusters from their X-ray luminosities.