2008/10/11 by Christopher A. Onken, Juna A. Kollmeier · 5 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/595746
10 pages including 4 figures, submitted to ApJL, incorporates referee's comments
arxiv created 2008/10/11 · openalex publication_date 2008/11/12 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present a method for obtaining accurate black hole (BH) mass estimates from the Mg II emission line in active galactic nuclei (AGNs). Employing the large database of AGN measurements from the Sloan Digital Sky Survey (SDSS) presented by Shen et al., we find that AGNs in the redshift range 0.3-0.9, for which a given object can have both Hβ and Mg II line widths measured, display a modest but correctable discrepancy in Mg II-based masses that correlates with the Eddington ratio. We use the SDSS database to estimate the probability distribution of the true (i.e., Hβ-based) mass given a measured Mg II line width. These probability distributions are then applied to the SDSS measurements from Shen et al. across the entire Mg II-accessible redshift range (0.3-2.2). We find that accounting for this residual correlation generally increases the dispersion of Eddington ratios by a small factor (~0.09 dex for the redshift and luminosity bins we consider). We continue to find that the intrinsic distribution of Eddington ratios for luminous AGNs is extremely narrow, 0.3-0.4 dex, as demonstrated by Kollmeier et al. Using the method we describe, Mg II emission lines can be used with confidence to obtain BH mass estimates.