The lick AGN monitoring project: Recalibrating single-epoch virial black hole mass estimates

Daeseong Park, Jong Hak Woo, Tommaso Treu, Aaron J. Barth, Misty C. Bentz, Vardha N. Bennert, Gabriela Canalizo, Alexei V. Filippenko, Elinor Gates, Jenny E. Greene, Matthew A. Malkan, Jonelle Walsh

Research output: Contribution to journalArticlepeer-review

84 Scopus citations

Abstract

We investigate the calibration and uncertainties of black hole (BH) mass estimates based on the single-epoch (SE) method, using homogeneous and high-quality multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN) Monitoring Project for nine local Seyfert 1 galaxies with BH masses <108 M . By decomposing the spectra into their AGNs and stellar components, we study the variability of the SE Hβ line width (full width at half-maximum intensity, FWHM or dispersion, σ) and of the AGN continuum luminosity at 5100 (L 5100). From the distribution of the "virial products" (∞ FWHM 2 L 0.5 5100 or σ 2 L 0.5 5100) measured from SE spectra, we estimate the uncertainty due to the combined variability as 0.05dex (12%). This is subdominant with respect to the total uncertainty in SE mass estimates, which is dominated by uncertainties in the size-luminosity relation and virial coefficient, and is estimated to be ∼0.46dex (factor of ∼3). By comparing the Hβ line profile of the SE, mean, and root-mean-square (rms) spectra, we find that the Hβ line is broader in the mean (and SE) spectra than in the rms spectra by ∼0.1dex (25%) for our sample with FWHM <3000kms-1. This result is at variance with larger mass BHs where the difference is typically found to be much less than 0.1dex. To correct for this systematic difference of the Hβ line profile, we introduce a line-width dependent virial factor, resulting in a recalibration of SE BH mass estimators for low-mass AGNs.

Original languageEnglish (US)
Article number30
JournalAstrophysical Journal
Volume747
Issue number1
DOIs
StatePublished - Mar 1 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • galaxies: Seyfert
  • galaxies: nuclei

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