Ultraluminous Quasars At High Redshift Show Evolution In Their Radio-Loudness Fraction In Both Redshift And Ultraviolet Luminosity

TL;DR

This study examines the evolution of radio-loudness in ultraluminous quasars at high redshift, finding that their radio-loud fraction aligns with previous models and extends understanding to earlier cosmic times.

Contribution

It provides the first measurement of radio-loud fraction for ultraluminous quasars at redshift 4.4-5.2, confirming its consistency with earlier trends at higher redshifts.

Findings

Radio-loud fraction is approximately 8.5% at high redshift.

The radio-loud fraction decreases with increasing redshift.

Results extend previous models to earlier cosmic epochs.

Abstract

We take a sample of 94 ultraluminous, optical quasars from the search of over 14,486 deg^2 by Onken et al. 2022 in the range 4.4<redshift<5.2 and match them against the Rapid ASKAP Continuum Survey (RACS) observed on the Australian Square Kilometre Array Pathfinder (ASKAP). From this most complete sample of the bright end of the redshift ~5 quasar luminosity function, there are 10 radio continuum detections of which 8 are considered radio-loud quasars. The radio-loud fraction for this sample is 8.5 \pm 2.9 per cent. Jiang et al. 2007 found that there is a decrease in the radio-loud fraction of quasars with increasing redshift and an increase with increasing absolute magnitude at rest frame 2500 Angstroms. We show that the radio-loud fraction of our quasar sample is consistent with that predicted by Jiang et al. 2007, extending their result to higher redshifts.