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

Brandon C. Kelly, Jill Bechtold

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

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
Volume168
Issue number1
DOIs
StatePublished - Jan 2007

Fingerprint

active galactic nuclei
time measurement
estimates
luminosity
regression analysis
continuums
distribution
reverberation
probe
quasars
estimating
simulation
probes

Keywords

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

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Virial masses of black holes from single epoch spectra of active galactic nuclei. / Kelly, Brandon C.; Bechtold, Jill.

In: Astrophysical Journal, Supplement Series, Vol. 168, No. 1, 01.2007, p. 1-18.

Research output: Contribution to journalArticle

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abstract = "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 {\AA}) 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.",
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