Discovery of a Low-redshift Hot Dust-obscured Galaxy

Abstract

We report the discovery of the hyperluminous, highly obscured active galactic nuclei (AGN) WISE J190445.04+485308.9 (W1904+4853, hereafter, L _bol ∼ 1.1 × 10 ^13 L _⊙ ) at z = 0.415. Its well-sampled spectral energy distribution (SED) is dominated by infrared dust emission, though broad emission lines are detected in the optical spectra. These features suggest that W1904+4853 contains an actively accreting supermassive black hole hidden in its dusty cocoon, resembling the observed properties of hot dust-obscured galaxies (Hot DOGs), a population previously only identified at z > 1.0. Using the broad component of the Mg ii 2798 Å emission line, we estimate a black hole mass of $\mathrm{log}({M}_{\mathrm{BH}}/{M}_{\odot })=8.4\pm 0.4$ . The corresponding Eddington ratio ( η ) of ${1.4}_{-0.7}^{+1.3}$ implies that the central black hole accretion is at the theoretical limit of isotropic accretion. The rest-frame UV-optical SED also indicates that the host galaxy of W1904+4853 harbors strong star formation activity at the rate of 6–84 M _⊙ yr ^−1 with an independent estimate of star formation rate up to ∼45 M _⊙ yr ^−1 using the [O ii ] emission line. With an estimated stellar mass of 3 × 10 ^10 M _⊙ , the host galaxy appears to be a starburst system with respect to the main sequence of the star-forming galaxies at the same redshift. Although blueshifted and asymmetric [O iii ] emission provides evidence of an outflow, we estimate it to be an order of magnitude smaller than the star formation rate, indicating that the current obscured AGN activity at the center has not yet produced significant feedback on the host galaxy star formation activity. W1904+4853 supports the interpretation that Hot DOGs are a rare transitional phase of AGN accretion in galaxy evolution, a phase that can persist into the present-day Universe.

Keywords

• Ultraluminous infrared galaxies
• Supermassive black holes
• Active galaxies