A Closer Look at Two of the Most Luminous Quasars in the Universe

Ultraluminous quasars (M 1450 ≤ -29) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341+1720 (M 1450 = -29.56, z = 3.71) and J2125-1719 (M 1450 = -29.39, z = 3.90), in the Extremely Luminous Quasar Survey (ELQS) and its extension to the Pan-STARRS 1 footprint (PS-ELQS), we herein present an analysis of their rest-frame UV to optical spectroscopy. Both quasars harbor very massive SMBHs with M BH =6.73 - 0.83+0.75 × 10 9, M ⊙ and M BH = 5.45 -0.55 +0.60 × 10 9, M ⊙, respectively, showing evidence of accretion above the Eddington limit ( and ). NOEMA 3 millimeter observations of J0341+1720 reveal a highly star-forming (SFR ≈ 1500 M o˙ yr-1), ultraluminous infrared galaxy (L IR ≈ 1.0 1013 L o˙) host, which, based on an estimate of its dynamical mass, is only ∼30 times more massive than the SMBH it harbors at its center. As examples of luminous super-Eddington accretion, these two quasars provide support for theories that explain the existence of billion solar mass SMBHs ∼700 million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.