Black Hole Masses and Eddington Ratios at 0.3 <z< 4

Abstract

We study the distribution of Eddington luminosity ratios, L bol /L Edd , of active galactic nuclei (AGNs) discovered in the AGN and Galaxy Evolution Survey (AGES). We combine H, Mg ii, and C iv line widths with continuum luminosities to estimate black hole ( BH ) masses in 407 AGNs, covering the redshift range z $ 0:3 Y 4 and the bolometric luminosity range L bol $ 10 45 Y10 47 ergs s À1. The sample consists of X-ray or mid-infrared (24 m) point sources with optical magnitude R 21:5 mag and optical emission-line spectra characteristic of AGNs. For the range of luminosity and redshift probed by AGES, the distribution of estimated Eddington ratios is well described as lognormal, with a peak at L bol /L Edd ' 1/4 and a dispersion of 0.3 dex. Since additional sources of scatter are minimal, this dispersion must account for contributions from the scatter between estimated and true BH mass and the scatter between estimated and true bolometric luminosity. Therefore, we conclude that (1) neither of these sources of error can contribute more than $0.3 dex rms, and (2) the true Eddington ratios of optically luminous AGNs are even more sharply peaked. Because the mass estimation errors must be smaller than $0.3 dex, we can also investigate the distribution of Eddington ratios at fixed BH mass. We show for the first time that the distribution of Eddington ratios at fixed BH mass is peaked, and that the dearth of AGNs at a factor of $10 below Eddington is real and not an artifact of sample selection. These results provide strong evidence that supermassive BHs gain most of their mass while radiating close to the Eddington limit, and they suggest that the fueling rates in luminous AGNs are ultimately determined by BH self-regulation of the accretion flow rather than galactic-scale dynamical disturbances.

The cosmic growth of the active black hole population at 1 <z <2 in zCOSMOS, VVDS and SDSS

“…For the combined sample, the observed distribution is approximately confined within the Eddington limit and λ = 0.01, consistent with previous results on type-1 AGN (e.g. Kollmeier et al 2006;Trump et al 2009;Schulze & Wisotzki 2010;Shen et al 2011). The Eddington limit serves as an upper boundary for the accretion rate of a BH.…”

“…by which amount these distributions are actually broadened by using viral masses instead of true masses. Several studies suggest this value is actually smaller, ∼ 0.2 dex (Kollmeier et al 2006;Fine et al 2008;Steinhardt & Elvis 2010;Kelly et al 2010). For a detailed discussion of this difference, its possible origin and consequences see e.g.…”

Triggering active galactic nuclei in hierarchical galaxy formation: disk instability vs. interactions

“…8) we face with a complex situation; in fact, the observational distributions (at least) depend on i) the method adopted to select AGN; ii) the adopted bolometric correction; iii) the method adopted to measure the BH mass (for a discussion of the above points, see, e.g., Netzer et al 2009a,b and references therein). This is illustrated in the top left-hand panel, where we compare with low-redshift data for AGN with L AGN < 10 4 6 erg s −1 taken from Hickox et al (2009) and Kollmeier et al (2006). The former refer to AGN at 0.25 < z < 0.8 selected in different wavebands.…”

“…The authors base their estimate M BH on the L B,bul − M BH relation after estimating the bulge luminosity of the host galaxy in the B band, while the bolometric luminosity for X-ray AGN are derived from the bolometric correction of Hopkins et al (2007); for radio AGNs that are not detected in X-rays, they used the X-ray stacking results to derive approximate upper limits on the X-ray AGN luminosity, while for IR AGNs that are not detected in X-rays, L bol is derived from the rest-frame 4.5 µm luminosity. We also compare this with data from Kollmeier et al (2006), derived from the AGES survey and consisting of X-ray (XBootes survey, Murray et al 2005 or mid-infrared (Eisenhardt et al 2004) point sources with optical magnitude R ≤ 21.5 mag and optical emission-line spectra characteristic of AGNs. Black hole masses were estimated using virial relationships and Hβ MgII, and CIV emission-line widths, while bolometric luminosities were estimated using the bolometric correction of Kaspi et al (2000) to the monochromatic luminosities at 5100 Å.…”

AGN and Host Galaxies in the COSMOS Survey

“…However Type 1 AGNs are limited to L/L E dd > 0.01, despite simulations which show that the COSMOS AGN detection limits would reveal Type 1 AGNs with L I /L E dd ∼ 10 −3 (Trump et al 2009b). Optical luminosity and accretion rate are correlated, such that more rapidly accretion AGNs tend to be more optically luminous, (see also Kollmeier et al 2006, Gavignaud et al 2008.…”