The eROSITA Final Equatorial-Depth Survey (eFEDS)

A multiwavelength view of WISE mid-infrared galaxies/active galactic nuclei

¹ Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
e-mail: toba@kusastro.kyoto-u.ac.jp
² Academia Sinica Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, AS/NTU, No.1, Sect. 4, Roo-sevelt Road, Taipei 10617, Taiwan
³ Research Center for Space and Cosmic Evolution, Ehime University, 2–5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
⁴ Department of Physics, Nara Women’s University, Kitauoyanishimachi, Nara, Nara 630-8506, Japan
⁵ Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching bei München, Germany
⁶ Leibniz-Institut für Astrophysik, Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
⁸ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁹ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, PR China
¹⁰ Dipartimento di Fisica e Astronomia, Università di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
¹¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
¹² Kagoshima University, Graduate School of Science and Engineering, Kagoshima 890-0065, Japan
¹³ Hokkaido University, Faculty of Science, Sapporo 060-0810, Japan
¹⁴ Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
¹⁵ Astronomical Institute, Tohoku University, 6–3 Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan
¹⁶ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
¹⁷ National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁸ Department of Astronomy, School of Science, The Graduate University for Advanced Studies, SOKENDAI, Mitaka, Tokyo 181-8588, Japan
¹⁹ Faculty of Science and Engineering, Kindai University, Higashi-Osaka, 577-8502, Japan
²⁰ Department of Economics, Management and Information Science, Onomichi City University, Hisayamada 1600-2, Onomichi, Hiroshima 722-8506, Japan
²¹ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

Received: 15 June 2021
Accepted: 24 August 2021

Abstract

Aims. We investigate the physical properties – such as the stellar mass (M_*), star-formation rate, infrared (IR) luminosity (L_IR), X-ray luminosity (L_X), and hydrogen column density (N_H) – of mid-IR (MIR) galaxies and active galactic nuclei (AGN) at z < 4 in the 140 deg² field observed by eROSITA on SRG using the Performance-and-Verification-Phase program named the eROSITA Final Equatorial Depth Survey (eFEDS).

Methods. By cross-matching the WISE 22 μm (W4)-detected sample and the eFEDS X-ray point-source catalog, we find that 692 extragalactic objects are detected by eROSITA. We have compiled a multiwavelength dataset extending from X-ray to far-IR wavelengths. We have also performed (i) an X-ray spectral analysis, (ii) spectral-energy-distribution fitting using X-CIGALE, (iii) 2D image-decomposition analysis using Subaru Hyper Suprime-Cam images, and (iv) optical spectral fitting with QSFit to investigate the AGN and host-galaxy properties. For 7088 WISE 22 μm objects that are undetected by eROSITA, we have performed an X-ray stacking analysis to examine the typical physical properties of these X-ray faint and probably obscured objects.

Results. We find that (i) 82% of the eFEDS–W4 sources are classified as X-ray AGN with log L_X > 42 erg s⁻¹ ; (ii) 67 and 24% of the objects have log(L_IR/L_⊙) > 12 and 13, respectively; (iii) the relationship between L_X and the 6 μm luminosity is consistent with that reported in previous works; and (iv) the relationship between the Eddington ratio and N_H for the eFEDS–W4 sample and a comparison with a model prediction from a galaxy-merger simulation indicates that approximately 5.0% of the eFEDS–W4 sources in our sample are likely to be in an AGN-feedback phase, in which strong radiation pressure from the AGN blows out the surrounding material from the nuclear region.

Conclusions. Thanks to the wide area coverage of eFEDS, we have been able to constrain the ranges of the physical properties of the WISE 22 μm-selected sample of AGNs at z < 4, providing a benchmark for forthcoming studies on a complete census of MIR galaxies selected from the full-depth eROSITA all-sky survey.