The Effect of Variability on the Estimation of Quasar Black Hole Masses

Abstract

We investigate the time-dependent variations of ultraviolet (UV) black hole mass estimates of quasars in the Sloan Digital Sky Survey (SDSS). From SDSS spectra of 615 high-redshift (1.69 < z < 4.75) quasars with spectra from two epochs, we estimate black hole masses, using a single-epoch technique which employs an additional, automated night-sky-line removal, and relies on UV continuum luminosity and CIV (1549A) emission line dispersion. Mass estimates show variations between epochs at about the 30% level for the sample as a whole. We determine that, for our full sample, measurement error in the line dispersion likely plays a larger role than the inherent variability, in terms of contributing to variations in mass estimates between epochs. However, we use the variations in quasars with r-band spectral signal-to-noise ratio greater than 15 to estimate that the contribution to these variations from inherent variability is roughly 20%. We conclude that these differences in black hole mass estimates between epochs indicate variability is not a large contributer to the current factor of two scatter between mass estimates derived from low- and high-ionization emission lines.

arXiv comment76 pages, 15 figures, 2 (long) tables; Accepted for publication in ApJ (November 10, 2007)

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• The Lick AGN Monitoring Project: Recalibrating Single-Epoch Virial Black Hole Mass Estimates
• Redshift Evolution in Black Hole-Bulge Relations: Testing CIV-based Black Hole Masses
• The Civ line width distribution for quasars and its implications for broad-line region dynamics and virial mass estimation
• Simultaneous Ultraviolet and Optical Emission-line Profiles of Quasars: Implications for Black Hole Mass Determination
• Black Hole Mass Estimates and Rapid Growth of Supermassive Black Holes in Luminous $z\sim$ 3.5 Quasars
• Constraining the quasar population with the broad-line width distribution
• Characterizing Quasar CIV Emission-line Measurements from Time-resolved Spectroscopy
• CIV emission line properties and uncertainties in black hole mass estimates of z ~ 3.5 quasars
• Peculiar Radio Structures in the Central Regions of Galaxy Cluster Abell 585
• Composite reverberation mapping