The lick AGN monitoring project: Alternate routes to a broad-line region radius

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

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


It is now possible to estimate black hole (BH) masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central BHs coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region (BLR). Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the BLR scales as the square root of the X-ray and Hβ luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the BLR correlates most tightly with Hβ luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of 2. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua.

Original languageEnglish (US)
Pages (from-to)409-416
Number of pages8
JournalAstrophysical Journal
Issue number1
StatePublished - Nov 1 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: Seyfert
  • Galaxies: active
  • Galaxies: nuclei


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