The eROSITA Final Equatorial-Depth Survey (eFEDS). The stellar counterparts of eROSITA sources identified by machine learning and Bayesian algorithms

Abstract

Stars are ubiquitous X-ray emitters and will be a substantial fraction of the X-ray sources detected in the on-going all-sky survey performed by the eROSITA instrument aboard the Spectrum Roentgen Gamma (SRG) observatory. We use the X-ray sources in the eROSITA Final Equatorial-Depth Survey (eFEDS) field observed during the SRG performance verification phase to investigate different strategies to identify the stars among other source categories. We focus here on Support Vector Machine (SVM) and Bayesian approaches, and our approaches are based on a cross-match with the Gaia catalog, which will eventually contain counterparts to virtually all stellar eROSITA sources. We estimate that 2060 stars are among the eFEDS sources based on the geometric match distance distribution, and we identify the 2060 most likely stellar sources with the SVM and Bayesian methods, the latter being named HamStars in the eROSITA context. Both methods reach completeness and reliability percentages of almost 90%, and the agreement between both methods is, incidentally, also about 90%. Knowing the true number of stellar sources allowed us to derive association probabilities $p_{ij}$ for the SVM method similar to the Bayesian method so that one can construct samples with defined completeness and reliability properties using appropriate cuts in $p_{ij}$. The thus identified stellar sources show the typical characteristics known for magnetically active stars, specifically, they are generally compatible with the saturation level, show a large spread in activity for stars of spectral F to G, and have comparatively high fractional X-ray luminosities for later spectral types.

13 pages, 11 figures. To appear on A&A, Special Issue: The Early Data Release of eROSITA and Mikhail Pavlinsky ART-XC on the SRG Mission

References in corpus (11)

• The Gaia mission
• The Radial Velocity Experiment (RAVE): first data release
• The eROSITA X-ray telescope on SRG
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• Probabilistic Cross-Identification of Astronomical Sources
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Identification and characterization of the counterparts to the point-like sources
• The eROSITA Final Equatorial-Depth Survey (eFEDS): The AGN Catalogue and its X-ray Spectral Properties
• Identification of Young Stellar Object candidates in the $Gaia$ DR2 x AllWISE catalogue with machine learning methods
• Catalogue of new Herbig Ae/Be and classical Be stars. A machine learning approach to Gaia DR2
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Presenting The Demographics of X-ray Emission From Normal Galaxies
• The eROSITA Final Equatorial-Depth Survey (eFEDS): The variability catalogue and multi-epoch comparison

Cited by in corpus (15)

• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Identification and characterization of the counterparts to the point-like sources
• Detecting clusters of galaxies and active galactic nuclei in an eROSITA all-sky survey digital twin
• The stellar content of the ROSAT all-sky survey
• The cosmic web of X-ray active galactic nuclei seen through the eROSITA Final Equatorial Depth Survey (eFEDS)
• Compact white-dwarf binaries in the combined SRG/eROSITA/SDSS eFEDS survey
• The eROSITA Final Equatorial Depth Survey (eFEDS): the hard X-ray selected sample
• $\mathrm{H}\alpha$ chromospheric activity of F-, G-, and K-type stars observed by the LAMOST Medium-Resolution Spectroscopic Survey
• ''Forbidden" stars in the eROSITA all-sky survey: X-ray emission from very late-type giants
• The eROSITA Final Equatorial Depth Survey (eFEDS): SDSS spectroscopic observations of X-ray sources
• X-raying the Sco-Cen OB association: The low-mass stellar population revealed by eROSITA
• Cross-correlation between soft X-rays and galaxies A new benchmark for galaxy evolution models
• SRG/eROSITA 3D mapping of the ISM using X-ray absorption spectroscopy
• Probing habitable regions with SRG/eROSITA