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 $M_{BH}={6.73}_{-0.83}^{+0.75}\times {10}^9{M}_{\odot }$ and $M_{BH}={5.45}_{-0.55}^{+0.60}\times {10}^9{M}_{\odot }$, respectively, showing evidence of accretion above the Eddington limit ($L_{bol}/L_{Edd}={2.74}_{-0.27}^{+0.39}$ and $L_{bol}/L_{Edd}={3.01}_{-0.30}^{+0.34}$). NOEMA 3 millimeter observations of J0341+1720 reveal a highly star-forming (SFR ≈ 1500 M _⊙ yr⁻¹), ultraluminous infrared galaxy (L _IR ≈ 1.0 × 10¹³ L _⊙) 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.