Virial masses of black holes from single epoch spectra of active galactic nuclei

Brandon C. Kelly, Jill Bechtold

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


We describe the general problem of estimating black hole masses of active galactic nuclei (AGNs) by calculating the conditional probability distribution of MBH given some set of observables. Special attention is given to the case where one uses the AGN continuum luminosity and emission line widths to estimate MBH, and we outline how to set up the conditional probability distribution of MBH given the observed luminosity, line width, and redshift. We show how to combine the broad-line estimates of M BH with information from an intrinsic correlation between M BH and L, and from the intrinsic distribution of MBH, in a manner that improves the estimates of MBH. Simulation was used to assess how the distribution of MBH inferred from the broad-line mass estimates differs from the intrinsic distribution, and we find that this can lead to an inferred distribution that is too broad. We use these results and a sample of 25 sources that have recent reverberation mapping estimates of AGN black hole masses to investigate the effectiveness of using the C IV emission line to estimate MBH and to indirectly probe the C IV region size-luminosity (R-L) relationship. A linear regression of log L λ (1549 Å) on log MBH found that L 1549 ∝ MBH1.17±0.22. A linear regression also found that MBH ∝ L1549 0.41±0.07FWHMC IV2, implying a C IV R-L relationship of the form RC IV ∝ L1549 0.41±0.07. Including the C IV line FWHM resulted in a reduction of a factor of ∼ 1/3 in the error in the estimates of M BH over simply using the continuum luminosity, statistically justifying its use. We estimated MBH from both C IV and Hβ for a sample of 100 sources, including new spectra of 29 quasars. We find that the two emission lines give consistent estimates if one assumes R ∝ L UV1/2 for both lines.

Original languageEnglish (US)
Pages (from-to)1-18
Number of pages18
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Jan 2007
Externally publishedYes


  • Galaxies: active
  • Line: profiles
  • Methods: data analysis
  • Methods: statistical
  • Quasars: emission lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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