The eROSITA Final Equatorial-Depth Survey (eFEDS)

The AGN catalog and its X-ray spectral properties^★

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching bei München, Germany
e-mail: liu@mpe.mpg.de
² Dipartimento di Fisica e Astronomia, Università di Bologna, Via Piero Gobetti 93/2, 40129 Bologna, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
⁴ Institute for Astronomy and Astrophysics, National Observatory of Athens, V. Paulou and I. Metaxa 11532 Greece
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁷ Dr. Karl Remeis-Sternwarte & Erlangen Centre for Astroparticle Physics, Sternwartstr. 7, 96049 Bamberg, Germany
⁸ Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606–8502, Japan
⁹ Academia Sinica Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, AS/NTU, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
¹⁰ Research Center for Space and Cosmic Evolution, Ehime University, 2–5 Bunkyo-cho, Matsuyama, Ehime 790–8577, Japan
¹¹ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980–8578, Japan
¹² Astronomical Institute, Tohoku University, Aramaki, Aoba-ku, Sendai, 980–8578 Miyagi, Japan
¹³ ICREA and Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
¹⁴ Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
¹⁵ National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

Received: 26 June 2021
Accepted: 21 March 2022

Abstract

Context. The eROSITA Final Equatorial Depth Survey (eFEDS), observed with eROSITA ahead of its planned 4-yr all-sky survey, is the largest contiguous-field X-ray survey at present. It yielded a large sample of X-ray sources with very rich multiband photometric and spectroscopic coverage.

Aims. We present here the eFEDS active galactic nuclei (AGN) catalog and the eROSITA X-ray spectral properties of the eFEDS sources.

Methods. Using a Bayesian method, we performed a systematic X-ray spectral analysis for all the eFEDS sources. We adopted multiple spectral models, including single-component power-law or hot-plasma models and double-component models of a power law plus soft excess. We investigated the capacity of eROSITA X-ray spectra for constraining AGN spectral shapes through a detailed analysis of the posterior parameter probability distribution functions. Hierarchical Bayesian modeling was used to recover the spectral parameter distribution of the sample. The source fluxes and luminosities were measured from the posterior of the spectral fitting.

Results. The eFEDS AGN catalog (22 079 sources) comprises ~80% of the eFEDS point sources. Despite a large number of faint sources, our spectral fitting provides reasonable measurements of spectral shapes and intrinsic luminosities for a majority of the sources. Because of sample selection bias, this AGN catalog is dominated by X-ray unobscured sources, with an obscured (logN_H > 21.5) fraction of 8%; the power-law emission of the hot corona is also relatively soft, with a typical slope of 2.0. For type-I AGN, the X-ray emission is well correlated with the UV emission with the usual anticorrelation between the X-ray to UV spectral slope α_OX and the UV luminosity. The X-ray spectral properties measured with various models are presented for all the eFEDS sources.