Discovery of the most luminous quasar of the last 9 Gyr

Abstract

We report the discovery of a bright (mag (AB), mag (Vega)) quasar at redshift-the optically brightest (unbeamed) quasar at 0.4$[]>. SMSS J114447.77-430859.3, at a Galactic latitude of, 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 Mg ii, H, H, and Pa emission lines, from which we measure a black hole mass of. With its high luminosity, or mag (AB), we estimate an Eddington ratio of. As the most luminous quasar known over the last 9 Gyr of cosmic history, having a luminosity greater than 3C 273, the source offers a range of potential follow-up opportunities.