Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper

TL;DR

This study identifies and characterizes the most luminous high-redshift quasars ($z>4.5$) in the Southern sky using SkyMapper, Gaia, and WISE data, significantly increasing the known sample of such quasars.

Contribution

It presents a new method combining colour selection with parallax and proper motion data to efficiently find high-redshift quasars over a large sky area.

Findings

Discovered 21 quasars at $z ext{≥}4$ in 12,500 deg$^2$ of Southern sky.

Increased the number of known bright $z ext{≥}4.5$ quasars in the Southern hemisphere from 10 to 26.

Total of 42 quasars with $R_p<18.2$ and $z ext{≥}4.5$ identified.

Abstract

The most luminous quasars at high redshift harbour the fastest-growing and most massive black holes in the early Universe. They are exceedingly rare and hard to find. Here, we present our search for the most luminous quasars in the redshift range from $z=4.5$ to $5$ using data from SkyMapper, Gaia and WISE. We use colours to select likely high-redshift quasars and reduce the stellar contamination of the candidate set with parallax and proper motion data. In $\sim$12,500~deg$^2$ of Southern sky, we find 92 candidates brighter than $R_p=18.2$. Spectroscopic follow-up has revealed 21 quasars at $z\ge 4$ (16 of which are within $z=[4.5,5]$), as well as several red quasars, BAL quasars and objects with unusual spectra, which we tentatively label OFeLoBALQSOs at redshifts of $z\approx 1$ to $2$. This work lifts the number of known bright $z\ge 4.5$ quasars in the Southern hemisphere from 10 to 26 and brings the total number of quasars known at $R_p<18.2$ and $z\ge 4.5$ to 42.