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

TL;DR

This study examines how time-dependent UV spectral variations affect quasar black hole mass estimates, finding that measurement errors and intrinsic variability contribute to observed differences but do not fully explain the scatter in mass estimates.

Contribution

It provides a quantitative analysis of variability's role in black hole mass estimation discrepancies using multi-epoch SDSS quasar spectra.

Findings

Mass estimate variations are about 30% between epochs.

Measurement error in line dispersion is a major source of variation.

Intrinsic variability contributes roughly 20% to mass estimate differences.

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.