XQR-30: Black Hole Masses and Accretion Rates of 42 z>6 Quasars

TL;DR

This study analyzes 42 high-redshift quasars to measure their black hole masses and accretion rates, revealing that early universe quasars host slightly less massive black holes that accrete more rapidly than their lower-redshift counterparts.

Contribution

First comprehensive analysis of black hole masses and accretion rates for 42 z>6 quasars using high-quality spectra, comparing them to lower-redshift samples.

Findings

Black hole masses range from 0.8 to 12 billion solar masses.

Eddington ratios are between 0.13 and 1.73, averaging 0.84.

High-redshift quasars have slightly less massive black holes but higher accretion rates than lower-redshift quasars.

Abstract

We present bolometric luminosities, black hole masses and Eddington ratios for 42 luminous quasars at z>6 using high signal-to-noise ratio VLT/X-Shooter spectra, acquired in the enlarged ESO Large Programme XQR-30. In particular, we derive bolometric luminosities from the rest-frame 3000 A, luminosities using a bolometric correction from the literature, and the black hole masses by modelling the spectral regions around the CIV 1549A and the MgII 2798A emission lines, with scaling relations calibrated in the local universe. We find that the black hole masses derived from both emission lines are in the same range, and the scatter of the measurements agrees with expectations from the scaling relations. The MgII-derived masses are between ~(0.8-12) x 10^9 Msun, and the derived Eddington ratios are within ~0.13-1.73, with a mean (median) of 0.84 (0.72). By comparing the total sample of quasars at z>5.8, from this work and from the literature, to a bolometric luminosity distribution-matched sample at z~1.5, we find that quasars at high redshift host slightly less massive black holes which accrete slightly more rapidly than at lower-z, with a difference in the mean Eddington ratios of the two samples of ~0.27, in agreement with recent literature work.