Black-hole masses of distant quasars

TL;DR

This paper reviews methods for estimating black hole masses in distant quasars, emphasizing the reliability of mass-scaling relations and presenting preliminary mass functions, highlighting rapid early universe growth and mass limits.

Contribution

It advocates for using mass-scaling relations for large quasar samples and provides preliminary black hole mass functions at high redshifts.

Findings

Black hole masses in distant quasars are typically 1-10 billion solar masses.

Black holes grow rapidly in the early universe, reaching a maximum around 10 billion solar masses.

Preliminary mass functions suggest a limit to black hole growth at high redshifts.

Abstract

A brief overview of the methods commonly used to determine or estimate the black hole mass in quiescent or active galaxies is presented and it is argued that the use of mass-scaling relations is both a reliable and the preferred method to apply to large samples of distant quasars. The method uses spectroscopic measurements of a broad emission-line width and continuum luminosity and currently has a statistical 1 sigma uncertainty in the absolute mass values of about a factor of 4. Potentially, this accuracy can be improved in the future. When applied to large samples of distant quasars it is evident that the black hole masses are very large, of order 1 to 10 billion solar masses, even at the highest redshifts of 4 to 6. The black holes must build up their mass very fast in the early universe. Yet they do not grow much larger than that: a maximum mass of about 10 billion solar masses is also observed. Preliminary mass functions of active black holes are presented for several quasar samples, including the Sloan Digital Sky Survey. Finally, common concerns related to the application of the mass scaling relations, especially for high redshift quasars, are briefly discussed.