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

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(LIR/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 MBH = 1010.92 M⊙ based on the broad Hα line: the host stellar mass is derived as M⋆ = 1013.55 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 MBH/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 NHint = 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.