Abstract
Abstract It is well known that reverberation mapping of active galactic nuclei (AGNs) reveals a relationship between AGN luminosity and the size of the broad-line region, and that use of this relationship, combined with the Doppler width of the broad emission line, enables an estimate of the mass of the black hole at the center of the active nucleus based on a single spectrum. An unresolved key issue is the choice of parameter used to characterize the line width, either FWHM or line dispersion (the square root of the second moment of the line profile). We argue here that use of FWHM introduces a bias, stretching the mass scale such that high masses are overestimated and low masses are underestimated. Here we investigate estimation of black hole masses in AGNs based on individual or “single-epoch” observations, with a particular emphasis in comparing mass estimates based on line dispersion and FWHM. We confirm the recent findings that, in addition to luminosity and line width, a third parameter is required to obtain accurate masses, and that parameter seems to be Eddington ratio. We present simplified empirical formulae for estimating black hole masses from the Hβ λ4861 and C iv λ1549 emission lines. While the AGN continuum luminosity at 5100 Å is usually used to predict the Hβ reverberation lag, we show that the luminosity of the Hβ broad component can be used instead without any loss of precision, thus eliminating the difficulty of accurately accounting for the host-galaxy contribution to the observed luminosity.
Highlights
The main results of this paper are as follows: 1. We confirm that the luminosity of the broad component of the Hβ emission line L (Hbbroad) is an excellent substitute for the AGN continuum luminosity rLeAvGeNrb(5er1a0ti0oÅn )lagfotr predicting (Hb)
We confirm that the line dispersion of the Hβ broad component sM(Hβ) and the FWHM for the Hβ broad component FWHMM(Hβ) in mean, or single-epoch, spectra are both reasonable proxies for the line dispersion of Hβ epoch viniritahleprrmodsuscptescmtrSuEm(HsβM).(HWβe) for find computing singlethat sM(Hβ) gives better results than FWHMM(Hβ), but both are usable
In the case of C IV emission-line lag t (C IV), we find that the line dispersion of the
Summary
1.1. Reverberation-based Black Hole MassesThe presence of emission lines with Doppler widths of thousands of kilometers per second is one of the defining characteristics of active galactic nuclei (AGNs; Burbidge & Burbidge 1967; Weedman 1976). It was long suspected that the21 Alfred P. Sloan Research Fellow.Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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