Hyper-luminous Dust Obscured Galaxies discovered by the Hyper Suprime-Cam on Subaru and WISE

Abstract

We present the photometric properties of a sample of infrared (IR) bright dust obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam (HSC) on the Subaru Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer (WISE), we discovered 48 DOGs with $i-K_{\mathrm{s}}>1.2$ and $i-[22]>7.0$, where $i$, $K_{\mathrm{s}}$, and [22] represent AB magnitude in the $i$-band, $K_{\mathrm{s}}$-band, and 22 $\hat{I}¼$m, respectively, in the GAMA 14hr field ($\sim$ 9 deg${}^2$). Among these objects, 31 ($\sim$ 65 %) show power-law spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show a NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma $z$ = 1.99 $\pm$ 0.45, we calculated their total IR luminosity using an empirical relation between 22 $\hat{I}¼$m luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5 $\pm$ 1.1) $\times$ $10^{13}$ L${}_{\odot }$, which classifies them as hyper-luminous infrared galaxies (HyLIRGs). We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22 $\hat{I}¼$m flux greater than 3.0 mJy and with $i$-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log $\ddot{I}•$ = -6.59 $\pm$ 0.11 [Mpc${}^{-3}$]. The IR LF for DOGs including data obtained from the literature is well fitted by a double-power law. The derived lower limit for the IR LD for our sample is $\ddot{I}{}_{\mathrm{IR}}$ $\sim$ 3.8 $\times$ 10${}^7$ [L${}_{\odot }$ Mpc${}^{-3}$] and its contributions to the total IR LD, IR LD of all ultra-luminous infrared galaxies (ULIRGs), and that of all DOGs are $>$ 3 %, $>$ 9 %, and $>$ 15 %, respectively.

15 pages, 15 figures, and 3 tables, accepted for publication in PASJ (Subaru special issue)