Eddington ratios of dust-obscured quasars at z ≲ 1: Evidence supporting dust-obscured quasars as young quasars

Abstract

Dust-obscured quasars have been suspected of being the intermediate-stage galaxies between merger-driven star-forming galaxies and unobscured quasars. This merger-driven galaxy evolution scenario suggests that dust-obscured quasars exhibit higher Eddington ratios (λ_{Edd) than those of unobscured quasars. However, their high dust obscuration poses challenges to accurately measuring their λEdd using commonly employed bolometric luminosity (Lbol) and black hole mass (MBH) estimators based on the ultraviolet or optical luminosity. Recently, new estimators for Lbol and MBH based on mid-infrared continuum luminosity (LMIR) were established, which are less affected by dust obscuration. These estimators enable the study of a large number of dust-obscured quasars across a wide redshift range. In this study, we measure the λEdd values of 30 dust-obscured quasars at z ≲ 1, the largest sample size to date, using the LMIR-based Lbol and MBH estimators. Our findings reveal that dust-obscured quasars exhibit significantly higher λEdd values compared to unobscured quasars. Moreover, we confirm that the enhanced λEdd values of dust-obscured quasars maintain consistency across the redshift span of 0 to 1. Our results strongly support the picture that dust-obscured quasars are in an earlier stage than unobscured quasars on the merger-driven galaxy evolutionary track.}