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

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Abstract

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.

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Notes

  1. The Russian eROSITA consortium is responsible for the analysis of the eROSITA data in the eastern half of the sky (in Galactic coordinates).

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ACKNOWLEDGMENTS

This study is based on observations with the eROSITA telescope onboard the SRG observatory. The SRG observatory was built by Roskosmos in the interests of the Russian Academy of Sciences represented by the Space Research Institute (IKI) within the framework of the Russian Federal Space Program, with the participation of the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The SRG/eROSITA X-ray telescope was built by a consortium of German institutes led by the Max-Planck-Institut für extraterrestrische Physik (MPE), and supported by DLR. The SRG spacecraft was designed, built, launched and is operated by the Lavochkin Association and its subcontractors. The science data are downlinked via the Deep Space Network Antennae in Bear Lakes, Ussurijsk, and Baykonur, funded by Roskosmos. The eROSITA data used in this paper were processed with the eSASS software developed by the German eROSITA consortium and the software developed by the Russian SRG/eROSITA consortium. The SRGz system was created at the High-Energy Astrophysics Department of the Space Research Institute of the Russian Academy of Sciences by the working group on the search for and identification of X-ray sources and the production of a catalog based on SRG/eROSITA data.

Funding

This work was supported by RSF grant no. 21-12-00343.

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Authors and Affiliations

  1. Space Research Institute, Russian Academy of Sciences, 117997, Moscow, Russia

    A. V. Meshcheryakov, G. A. Khorunzhev, S. A. Voskresenskaya, P. S. Medvedev, M. R. Gilfanov & R. A. Sunyaev

  2. Moscow State University, 119991, Moscow, Russia

    A. V. Meshcheryakov

  3. National Research University ‘‘Higher School of Economics’’, 101100, Moscow, Russia

    S. A. Voskresenskaya

  4. Max Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 1317, D-85741, Garching, Germany

    M. R. Gilfanov & R. A. Sunyaev

Authors
  1. A. V. Meshcheryakov
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  2. G. A. Khorunzhev
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  3. S. A. Voskresenskaya
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  4. P. S. Medvedev
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  5. M. R. Gilfanov
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  6. R. A. Sunyaev
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Correspondence to A. V. Meshcheryakov.

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Translated by V. Astakhov

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Meshcheryakov, A.V., Khorunzhev, G.A., Voskresenskaya, S.A. et al. SRGz: Classification of eROSITA Point X-ray Sources in the 1\({\%}\)DESI Region and Calibration of Photometric Redshifts*. Astron. Lett. 49, 646–661 (2023). https://doi.org/10.1134/S1063773723110129

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