Discovery of the most luminous quasar of the last 9 Gyr

TL;DR

This paper reports the discovery of the most luminous quasar in the last 9 billion years, with detailed spectral analysis revealing its black hole mass and high Eddington ratio, highlighting its significance for cosmic history studies.

Contribution

It presents the identification and characterization of the brightest known quasar at z > 0.4, including its luminosity, black hole mass, and accretion properties, expanding understanding of luminous quasars over cosmic time.

Findings

Most luminous quasar in last 9 Gyr identified

Black hole mass estimated at ~2.5 billion solar masses

Eddington ratio approximately 1.4

Abstract

We report the discovery of a bright (g = 14.5 mag (AB), K = 11.9 mag (Vega)) quasar at redshift z = 0.83 -- the optically brightest (unbeamed) quasar at z > 0.4. SMSS J114447.77-430859.3, at a Galactic latitude of b = +18.1deg, was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad MgII, H-beta, H-alpha, and Pa-beta emission lines, from which we measure a black hole mass of log10(M_BH/M_Sun) = 9.4 +/- 0.5. With its high luminosity, L_bol = (4.7 +/- 1.0) * 10^47 erg/s or M_i(z=2) = -29.74 mag (AB), we estimate an Eddington ratio of ~1.4. As the most luminous quasar known over the last ~9 Gyr of cosmic history, having a luminosity 8 times greater than 3C 273, the source offers a range of potential follow-up opportunities.