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

Abstract

Ultra-luminous quasars ($M_{1450}\le -29$) 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 $M_{\mathrm{BH}}=6.73_{-0.83}^{+0.75}\times 10^9{M}_{\odot }$ and $M_{\mathrm{BH}}=5.45_{-0.55}^{+0.60}\times 10^9{M}_{\odot }$, respectively, showing evidence of accretion above the Eddington limit ($L_{\mathrm{bol}}/L_{\mathrm{Edd}}=2.74_{-0.27}^{+0.39}$ and $L_{\mathrm{bol}}/L_{\mathrm{Edd}}=3.01_{-0.30}^{+0.34}$). NOEMA 3 millimeter observations of J0341$+$1720 reveal a highly star-forming ($\mathrm{SFR}\approx 1500{\mathrm{M}}_{\odot }{\mathrm{yr}}^{-1}$), ultra-luminous infrared galaxy ($L_{\mathrm{TIR}}\approx 1.0\times 10^{13}{L}_{\odot }$) host, which, based on an estimate of its dynamical mass, is only $\sim 30$ 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, which explain the existence of billion solar mass SMBHs $\sim 700$ million years after the Big Bang by moderate super-Eddington growth from standard SMBH seeds.

Accepted for publication in the Astrophysical Journal (ApJ)