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

¹ Department of Earth Sciences, Pusan National University, Busan 46241, Republic of Korea
² Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea
³ SNU Astronomy Research Center (SNU ARC), Astronomy Program, Dept. of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea
⁴ Department of Physics, Middlebury College, Middlebury, VT 05753, USA
⁵ Department of Astronomy and Atmospheric Sciences, College of Natural Sciences, Kyungpook National University, Daegu 41566, Republic of Korea
⁶ Leibniz-Institut für Astrophysik, Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 8 April 2024
Accepted: 6 August 2024

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 λ_Edd using commonly employed bolometric luminosity (L_bol) and black hole mass (M_BH) estimators based on the ultraviolet or optical luminosity. Recently, new estimators for L_bol and M_BH based on mid-infrared continuum luminosity (L_MIR) 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 λ_Edd values of 30 dust-obscured quasars at z ≲ 1, the largest sample size to date, using the L_MIR-based L_bol and M_BH estimators. Our findings reveal that dust-obscured quasars exhibit significantly higher λ_Edd values compared to unobscured quasars. Moreover, we confirm that the enhanced λ_Edd 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.