SRGz: Classification of eROSITA Point X-ray Sources in the 1\({\%}\)DESI Region and Calibration of Photometric Redshifts*

We consider the population of point X-ray sources from the two-year SRG/eROSITA survey in the 1\(\%\) DESI spectroscopic survey region in the eastern Galactic hemisphere (eROSITA–1\(\%\)DESI–East). The data under consideration combine a large survey area (compared to the medium-format Stripe82X and XMM-XXL X-ray surveys) and a record high completeness of spectroscopy for the optical counterparts of X-ray sources. We compare the results of the photometric (SRGz) and spectroscopic/astrometric (DESI EDR, SDSS, HELP, GAIA) measurements of the classes and redshifts of objects in three X-ray-flux-limited eROSITA–1\(\%\)DESI–East samples: \(F_{X,0.5-2}\geqslant 4\times 10^{-14}\) erg s\({}^{-1}\) cm\({}^{-2}\) (bright), \(F_{X,0.5-2}=(1.5{-}4)\times 10^{-14}\) erg s\({}^{-1}\) cm\({}^{-2}\) (medium), and \(F_{X,0.5-2}=(0.6{-}1.5)\times 10^{-14}\) erg s\({}^{-1}\) cm\({}^{-2}\) (faint) with a total area of 91.4, 91.4, and 16.62 deg\({}^{2}\), respectively. We propose a new method of postprocessing the probabilistic photo-z predictions based on a two-temperature correction of the probability density function \(PDF(z)\). This approach allows the calibration of the probabilistic predictions and confidence intervals of the photometric redshifts for eROSITA X-ray sources obtained by SRGz to be improved significantly.