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Description
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 H{beta} and H{alpha} spectral regions, which are lacking in Quasar Data Release 12 (DR12Q). We estimate the virial black hole mass from broad H{alpha} and/or H{beta}, and infer quasar redshifts from [OIII]{lambda}5007 emission lines. All the measurements and derived quantities are publicly available. A comparison between [OIII]{lambda}5007 redshifts and the visual inspection redshifts included in DR12Q indicates that the visual inspection redshifts are robust. We find that the full widths at half maximum of the broad H{alpha} are consistent with those of the broad H{beta}, while both the equivalent widths and line luminosities of the broad H{alpha} are obviously larger than the corresponding quantities of the broad H{beta}. We also find that there is an obviously systematic offset between the H{beta} and H{alpha} based mass if they are inferred from the empirical relationships in the literature. Using our large quasar sample, we have improved the H{beta} and H{alpha} based mass estimators by minimizing the difference between the H{beta}- and H{alpha}-based masses. For the black hole mass estimator (Equation (1)), we find that the coefficients (a,b)=(7.00,0.50) for H{alpha} and (a,b)=(6.96,0.50) for H{beta} are the best choices.
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