Eddington Ratios of Dust-Obscured Quasars at z 2

In the merger-driven galaxy evolution scenario, dust-obscured quasars are considered to be an intermediate population between merger-driven star-forming galaxies and unobscured quasars; however, this scenario is still controversial. To verify this, it is necessary to investigate whether dust-obscured quasars have higher Eddington ratio (λ_Edd) values than those of unobscured quasars, as expected in the merger-driven galaxy evolution scenario. In this study, we derive black hole (BH) masses of 10 dust-obscured quasars at z ~ 2, during the peak period of star-formation and BH growth in the Universe, using a newly derived mid-infrared (MIR) continuum luminosity L_MIR-based estimator that is highly resistant to dust extinction. Then, we compare the λ_Edd values of these dust-obscured quasars to those of unobscured type-1 quasars at similar redshifts. We find that the measured log(λ_Edd) values of the dust-obscured quasars, –0.06±0.10, are significantly higher than those of the unobscured quasars, -0.86±0.01. This result remains consistent across the redshift range from 1.5 to 2.5. Our results show that the dust-obscured quasars are at their maximal growth, consistent with the expectation from the merger-driven galaxy evolution scenario at the epoch quasar activities were most prominent in the cosmic history.