The Quasar Mass-Luminosity Plane I: A Sub-Eddington Limit for Quasars

TL;DR

This study analyzes a large quasar sample to reveal a sub-Eddington luminosity limit for high-mass quasars, challenging existing models and highlighting new theoretical puzzles in black hole accretion physics.

Contribution

It provides the first large-scale empirical evidence of a sub-Eddington limit for high-mass quasars across a wide redshift range.

Findings

Most luminous low-mass quasars reach Eddington luminosity.

High-mass quasars are systematically below their Eddington limit.

Measurement uncertainties cannot explain the observed luminosity shortfall.

Abstract

We use 62185 quasars from the Sloan Digital Sky Survey Data Release 5 sample to explore the relationship between black hole mass and luminosity. Black hole masses were estimated based on the widths of their H{\beta}, MgII and CIV lines and adjacent continuum luminosities using standard virial mass estimate scaling laws. We find that, over the range 0.2 < z < 4.0, the most luminous low-mass quasars are at their Eddington luminosity, but the most luminous high-mass quasars in each redshift bin fall short of their Eddington luminosities, with the shortfall of the order of 10 or more at 0.2 < z < 0.6. We examine several potential sources of measurement uncertainty or bias and show that none of them can account for this effect. We also show the statistical uncertainty in virial mass estimation to have an upper bound of ~0.15 dex, smaller than the 0.4 dex previously reported. We also examine the highest mass quasars in every redshift bin in an effort to learn more about quasars that are about to cease their luminous accretion. We conclude that the quasar mass-luminosity locus contains a number of new puzzles that must be explained theoretically.