Optical properties of infrared-bright dust-obscured galaxies viewed with Subaru Hyper Suprime-Cam

TL;DR

This study investigates the optical properties of IR-bright dust-obscured galaxies using Subaru HSC data, revealing their color characteristics, AGN activity, and a rare blue-excess phenomenon linked to AGN leakage.

Contribution

It provides the first large-scale optical analysis of IR-bright DOGs, identifying their color distributions, AGN dominance, and discovering blue-excess DOGs indicating AGN leakage.

Findings

IR-bright DOGs are redder than ULIRGs at similar redshifts.

Star-formation dominated DOGs are redder; AGN-dominated DOGs are bluer.

Eight DOGs show significant blue excess, suggesting leaked AGN emission.

Abstract

We report on the optical properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that are defined as (i-[22])_AB > 7.0. Because supermassive black holes (SMBHs) in IR-bright DOGs are expected to be rapidly growing in the major merger scenario, they provide useful clues for understanding the co-evolution of SMBHs and their host galaxies. However, the optical properties of IR-bright DOGs remain unclear because the optical emission of a DOG is very faint. By combining ~ 105 deg^2 images of the optical, near-IR, and mid-IR data obtained from the Subaru Hyper Suprime-Cam (HSC) survey, the VISTA VIKING survey, and the WISE all-sky survey, respectively, 571 IR-bright DOGs were selected. We found that IR-bright DOGs show a redder (g-z)_AB color than other populations of dusty galaxies, such as ultra-luminous IR galaxies (ULIRGs) at a similar redshift, with a significantly large dispersion. Among the selected DOGs, star-formation (SF) dominated DOGs show a relatively red color, while active galactic nucleus (AGN) dominated DOGs show a rather blue color in optical. This result is consistent with the idea that the relative AGN contribution in the optical emission becomes more significant at a later stage in the major merger scenario. We discovered eight IR-bright DOGs showing a significant blue excess in blue HSC bands (BluDOGs). This blue excess can be interpreted as a leaked AGN emission that is either a directly leaking or a scattered AGN emission, as proposed for some blue-excess Hot DOGs in earlier studies.