Eddington ratios of faint AGN at intermediate redshift: Evidence for a population of half-starved black holes

TL;DR

This study analyzes faint AGN at intermediate redshifts, revealing a significant population of black holes accreting at rates well below their Eddington limit, suggesting they are in a declining phase of activity.

Contribution

It provides the first detailed virial mass estimates for faint AGN at intermediate redshifts and identifies a population of half-starved black holes, supporting theories of AGN evolution.

Findings

Many low-luminosity AGN have L_bol/L_Edd < 0.1

Black holes at these luminosities may be in a decaying phase

Enhanced dispersion in the mass-luminosity relation at low luminosities

Abstract

We use one of the deepest spectroscopic samples of broad line active galactic nuclei (AGN) currently available, extracted from the VIMOS VLT Deep Survey (VVDS), to compute MgII and CIV virial masses estimate of 120 super-massive black holes in the redshift range 1.0<z<1.9 and 2.6<z<4.3. We find that the mass-luminosity relation shows considerably enhanced dispersion towards low AGN luminosities (log L_bol ~ 45). At these luminosities, there is a substantial fraction of black holes accreting far below their Eddington limit (L_bol/L_Edd < 0.1), in marked contrast to what is generally found for AGN of higher luminosities. We speculate that these may be AGN on the decaying branch of their light-curves, well past their peak activity. This would agree with recent theoretical predictions of AGN evolution. In the electronic Appendix of this paper we publish an update of the VVDS type-1 AGN sample, including the first and most of the second epoch observations. This sample contains 298 objects of which 168 are new.