Ultra-luminous high-redshift quasars from SkyMapper -- II. New quasars and the bright end of the luminosity function

TL;DR

This study discovers 142 new ultra-luminous high-redshift quasars using SkyMapper and other surveys, and measures the bright end of the QSO luminosity function at z=4.7-5.4, providing new insights into early universe black hole growth.

Contribution

It presents the first large, highly complete sample of high-redshift ultra-luminous quasars and derives the bright end of their luminosity function at multiple wavelengths.

Findings

142 new high-redshift quasars discovered.

Measured the slope of the bright end of the luminosity function as approximately -3.6.

Constructed the first z~5 QSO luminosity function at 300 nm.

Abstract

We search for ultra-luminous Quasi-Stellar Objects (QSOs) at high redshift using photometry from the SkyMapper Southern Survey Data Release 3 (DR3), in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 142 newly discovered Southern QSOs at $3.8<z<5.5$, of which 126 have $M_{145} <-27$ ABmag and are found in a search area of 14,486 deg$^2$. This Southern sample, utilising the Gaia astrometry to offset wider photometric colour criteria, achieves unprecedented completeness for an ultra-luminous QSO search at high redshift. In combination with already known QSOs, we construct a sample that is $>80$ per cent complete for $M_{145}<-27.33$ ABmag at $z=4.7$ and for $M_{145}<-27.73$ ABmag at $z=5.4$. We derive the bright end of the QSO luminosity function at restframe 145 nm for $z=4.7-5.4$ and measure its slope to be $\beta = -3.60\pm0.37$ and $\beta = -3.38\pm0.32$ for two different estimates of the faint-end QSO density adopted from the literature. We also present the first $z\sim 5$ QSO luminosity function at restframe 300 nm.