Supermassive black holes are growing slowly by $z\sim5$

Understand

We investigate the black hole mass function at $z\sim5$ using XQz5, our recent sample of the most luminous quasars between the redshifts $4.5 < z < 5.3$.

• We include 72 quasars with black hole masses estimated from velocity-broadened emission-line measurements and single-epoch virial prescriptions in the footprint of a highly complete parent survey.
• The sample mean Eddington ratio and standard deviation is $\log\lambda \approx -0.20\pm0.24$.
• The completeness-corrected mass function is modelled as a double power-law, and we constrain its evolution across redshift assuming accretion-dominated mass growth.