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

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.

Submitted to MNRAS, 10 pages

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• Forecasting cosmic acceleration measurements using the Lyman-$\alpha$ forest
• Quasar UV Luminosity Function at $3.5<z<5.0$ from SDSS Deep Imaging Data
• A Closer Look at Two of the Most Luminous Quasars in the Universe
• The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data
• Near-infrared spectroscopy of extreme BAL QSOs from the QUBRICS bright quasar survey