AN ULTRA-LUMINOUS QUASAR AT z = 5.363 WITH A TEN BILLION SOLAR MASS BLACK HOLE AND A METAL-RICH DLA AT z ∼ 5

We report the discovery of an ultra-luminous quasar J030642.51+185315.8 (hereafter J0306+1853) at redshift 5.363, which hosts a supermassive black hole with M_BH = (1.07 ± 0.27) × 10¹⁰ M_⊙. With an absolute magnitude M₁₄₅₀ = -28.92 and a bolometric luminosity L_bol ∼ 3.4 × 10¹⁴ L_⊙, J0306+1853 is one of the most luminous objects in the early universe. It is not likely to be a beamed source based on its small flux variability, low radio loudness, and normal broad emission lines. In addition, a z = 4.986 damped Lyα system (DLA) with [M/H] = -1.3 ± 0.1, among the most metal-rich DLAs at z ≳ 5, is detected in the absorption spectrum of this quasar. This ultra-luminous quasar puts strong constraints on the bright end of the quasar luminosity function and massive end of the black hole mass function. It will provide a unique laboratory for the study of BH growth and the co-evolution between a BH and the host galaxy with multi-wavelength follow-up observations. The future high-resolution spectra will give more insight into the DLA and other absorption systems along the line of sight of J0306+1853.