  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.
