A catalog of quasar properties from the Baryon Oscillation Spectroscopic Survey

TL;DR

This paper provides a detailed catalog of quasar spectral properties from the Baryon Oscillation Spectroscopic Survey, improving black hole mass estimators and validating redshift measurements using emission lines.

Contribution

It offers new measurements of quasar spectral features, compares different emission line-based redshifts, and refines black hole mass estimation methods using a large quasar sample.

Findings

Halpha and Hbeta FWHMs are consistent

Systematic offset between Hbeta and Halpha mass estimates

Improved mass estimators with optimized coefficients

Abstract

Using the quasars with z_em < 0.9 from the Baryon Oscillation Spectroscopic Survey, we measure the spectral characteristics, including continuum and emission lines, around the Hbeta and Halpha spectral regions, which are lacking in Quasar Data Release 12 (DR12Q). We estimate the virial black hole mass from broad Halpha and/or \hbeta, and infer quasar redshifts from O III5007 emission lines. All the measurements and derived quantities are publicly available. The comparison between O III5007 based redshifts and the visual inspection redshifts included in DR12Q indicates that the visual inspection redshifts are robust. We find that the FWHMs of the broad Halpha are consistent with those of the broad Hbeta, while both the equivalent widths and line luminosities of the broad Halpha are obviously larger than the corresponding quantities of the broad Hbeta. We also find that there is an obviously systematic offset between the Hbeta and Halpha based mass if they are inferred from the empirical relationships in the literature. Using our large quasar sample, we have improved the Hbeta and Halpha based mass estimators by minimizing the difference between the Hbeta- and Halpha-based mass. For the black hole mass estimator (Equation (1)), we find that the coefficients (a,b)=(7.00,0.50) for the Halpha and (a,b)=(6.96,0.50) for the Hbeta are the best choices.