SRG/eROSITA Survey in the Lockman Hole: Classification of X-ray Sources

TL;DR

This study classifies X-ray sources detected by SRG/eROSITA in the Lockman Hole into Galactic and extragalactic objects using flux ratios and optical data, achieving high accuracy and constructing number count curves.

Contribution

It introduces a classification method for SRG/eROSITA X-ray sources based on flux ratios and optical extent, with high reliability metrics.

Findings

High recall and precision for extragalactic sources (99.9% and 98.9%)

High recall and precision for Galactic sources (91.6% and 99.7%)

Constructed cumulative number counts for classified sources

Abstract

We have classified the point-like X-ray sources detected by the SRG/eROSITA telescope in the deep Lockman Hole survey. The goal was to separate the sources into Galactic and extragalactic objects. In this work have used the results of our previous cross-match of X-ray sources with optical catalogs. To classify SRG/eROSITA sources we have used the flux ratio $F_{x}/F_{o}$ and information about the source optical extent. As a result, of the 6885 X-ray sources in the eROSITA catalog 357 sources have been classified as Galactic and 5929 and as extragalactic. 539 out of 6885 have been treated as hostless, i.e., having no optical counterparts in the optical catalogs under consideration. 60 have remained unclassified due to the insufficient reliability of optical photometry. Recall and precision for the extragalactic sources are 99.9 and 98.9% (respectively) and 91.6 and 99.7% for the Galactic sources. Using this classification, we have constructed the curves of cumulative number counts for the Galactic and extragalactic sources in the Lockman Hole field. The code that accompanies this paper is available at https://github.com/mbelveder/ero-lh-class.git.