Oral Presentation
Extreme nature of blue-excess dust-obscured galaxies revealed by optical spectroscopy
Presenter: Akatoki Noboriguchi (Tohoku Univ.)
We report optical spectroscopic observations of four blue-excess dust-obscured galaxies (BluDOGs) identified by Subaru Hyper Suprime-Cam. BluDOGs are a sub-class of dust-obscured galaxies (DOGs, defined with the extremely red color, showing a significant flux excess in the optical g- and r-bands over the power-law fits to the fluxes at the longer wavelengths. Noboriguchi et al. (2019) has suggested that BluDOGs may correspond to the blowing-out phase involved in a gas-rich major merger scenario. However the detailed properties of BluDOGs are not understood because of the lack of spectroscopic information. In this work, we carry out deep optical spectroscopic observations of four BluDOGs using Subaru/FOCAS and VLT/FORS2. The obtained spectra show broad emission lines with extremely large equivalent widths, and a blue wing in the CIV line profile. The averaged rest-frame equivalent widths of the CIV lines are about 150 angstrom, about 6 times higher than the average of a typical type-1 quasar. The inferred Eddington ratios of the BluDOGs are higher than 1, suggesting that the BluDOGs are in a rapidly evolving phase of supermassive black holes.
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