Letter to the Editor

Ratio of black hole to galaxy mass of an extremely red dust-obscured galaxy at z = 2.52

¹ Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy
e-mail: matsuoka@arcetri.astro.it
² INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
³ Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
⁴ Academia Sinica Institute of Astronomy and Astrophysics, No. 1, Section 4, Roosevelt Rord, Taipei 10617, Taiwan
⁵ Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
⁶ Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
⁷ ICREA and Institut de Ciències del Cosmos, Universitat de Barcelona, Martí i Franquès, 1, 08028 Barcelona, Spain
⁸ National Astronomical Observatory of Japan (NAOJ), National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 24 July 2018
Accepted: 12 October 2018

Abstract

We present a near-infrared (NIR) spectrum of WISE J104222.11+164115.3, an extremely red dust-obscured galaxy (DOG), which has been observed with the Long-slit Intermediate Resolution Infrared Spectrograph (LIRIS) on the 4.2m William Hershel Telescope. This object was selected as a hyper-luminous DOG candidate at z ∼ 2 by combining the optical and IR photometric data based on the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE), although its redshift had not yet been confirmed. Based on the LIRIS observation, we confirmed its redshift of 2.521 and total IR luminosity of log(L_IR/L_⊙) = 14.57, which satisfies the criterion for an extremely luminous IR galaxy (ELIRG). Moreover, we indicate that this object seems to have an extremely massive black hole with M_BH = 10^10.92 M_⊙ based on the broad Hα line: the host stellar mass is derived as M_⋆ = 10^13.55 M_⊙ by a fit of the spectral energy distribution. Very recently, it has been reported that this object is an anomalous gravitationally lensed quasar based on near-IR high-resolution imaging data obtained with the Hubble Space Telescope. Its magnification factor has also been estimated with some uncertainty (i.e., μ = 53−122). We investigate the ratio of the black hole to galaxy mass, which is less strongly affected by a lensing magnification factor, instead of the absolute values of the luminosities and masses. We find that the M_BH/M_⋆ ratio (i.e., 0.0140–0.0204) is significantly higher than the local relation, following a sequence of unobscured quasars instead of obscured objects (e.g., submillimeter galaxies) at the same redshift. Moreover, the LIRIS spectrum shows strongly blueshifted oxygen lines with an outflowing velocity of ∼1100 km s⁻¹, and our Swift X-ray observation also supports that this source is an absorbed AGN with an intrinsic column density of N_H^int = 4.9 × 10²³ cm⁻². These results imply that WISE J104222.11+164115.3 is in a blow-out phase at the end of the buried rapid black hole growth.