The X-ray statistical properties of dust-obscured galaxies detected by eROSITA

¹ School of General Education, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
² Global Center for Science and Engineering, Faculty of Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
³ Department of Physics, School of Advanced Science and Engineering, Faculty of Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
⁴ Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Academia Sinica Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, AS/NTU, No.1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
⁷ Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
⁸ Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, Garching bei, München 85748, Germany
⁹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
¹⁰ Department of Economics, Management, and Information Science, Onomichi City University, Hisayamada 1600-2, Onomichi, Hiroshima 722-8506, Japan
¹¹ Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
¹² Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Kyoto 606-8502, Japan
¹³ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
¹⁴ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, Bologna 40129, Italy
¹⁵ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, Bologna 40129, Italy
¹⁶ Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
¹⁷ Gemini Observatory/NSF’s NOIRLab, 670 N. A’ohoku Place, Hilo HI 96720, USA
¹⁸ Leibniz-Institut für Astrophysik, Potsdam, An der Sternwarte 16, Potsdam 14482, Germany

^⋆ Corresponding authors: noboriguchi@astr.tohoku.ac.jp, kohei.ichikawa@aoni.waseda.jp

Received: 30 March 2024
Accepted: 7 April 2025

Abstract

Context. The tight correlation between supermassive black hole (SMBH) and host galaxy masses suggests their coevolution. Dust-obscured galaxies (DOGs) are thought to represent this coevolution phase, with active galactic nuclei (AGNs) buried in dust and gas. Despite hosting rapidly growing SMBHs, the X-ray statistical properties of DOGs remain poorly understood due to their rarity and the lack of wide, uniformly sensitive X-ray surveys.

Aims. We construct a sample of X-ray-detected DOGs in the eROSITA Final Equatorial Depth Survey (eFEDS) field and examine their X-ray statistical properties.

Methods. To construct the DOGs sample, we combined data from the Subaru/HSC SSP (optical), VIKING (near-infrared), and WISE (mid-infrared) all-sky surveys. We then cross-matched the sample with eROSITA-detected sources to select X-ray-detected DOGs.

Results. We report the discovery of 5738 IR-bright DOGs within the 60 deg² area covered by both eFEDS and VIKING, including 65 X-ray-detected DOGs (eFEDS-DOGs). Among these, 41 eFEDS-DOGs exhibit a near- to mid-IR power-law slope, indicating dust-obscured AGNs. Hydrogen column densities (N_H) of eFEDS-DOGs span 10²⁰ < N_H/cm⁻² ≲ 10²³, including even unobscured AGNs. Most IR-bright DOGs remain undetected in X-rays, implying heavy obscuration (N_H/cm⁻² > 10²³). eFEDS-DOGs, identified via the wide-area eROSITA survey, represent a less obscured DOG phase, possibly tracing the decline of dust/gas obscuration due to AGN feedback such as gas stripping or outflows. Some eFEDS-DOGs deviate up to ∼1 dex below the L_6 μm–L_{0.5 − 2 keV}^{(abs, corr)} relation, potentially indicating high Eddington ratios near the Eddington limit. This suggests that eFEDS-DOGs are promising candidates for rapidly growing black holes in an early AGN feedback phase.