COMPARING SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATORS FOR LUMINOUS QUASARS

By Yue Shen, Xin Liu. 2012

155 citations recorded by the source corpus.

Single-epoch virial black hole (BH) mass estimators utilizing broad emission lines have been routinely applied to high-redshift quasars to estimate their BH masses. Depending on the redshift, different line estimators (Hα, Hβ, Mg ii λ2798, C iv λ1549) are often used with optical/near-infrared spectroscopy. Here, we use a homogeneous sample of 60 intermediate-redshift (z ∼ 1.5–2.2) Sloan Digital Sky Survey quasars with optical and near-infrared spectra covering C iv through Hα to investigate the consistency between different single-epoch virial BH mass estimators. We critically compare rest-frame UV line estimators (C iv λ1549, C iii] λ1908, and Mg ii λ2798) with optical estimators (Hβ and Hα) in terms of correlations between line widths and between continuum/line luminosities, for the high-luminosity regime (L5100 > 1045.4 erg s−1) probed by our sample. The continuum luminosities of L1350 and L3000, and the broad-line luminosities are well correlated with L5100, reflecting the homogeneity of quasar spectra in the rest-frame UV–optical, among which L1350 and the line luminosities for C iv and C iii] have the largest scatter in the correlation with L5100. We found that the Mg ii FWHM correlates well with the FWHMs of the Balmer lines and that the Mg ii line estimator can be calibrated to yield consistent virial mass estimates with those based on the Hβ/Hα estimators, thus extending earlier results on less luminous objects. The C iv FWHM is poorly correlated with the Balmer line FWHMs, and the scatter between the C iv and Hβ FWHMs consists of an irreducible part (∼0.12 dex), and a part that correlates with the blueshift of the C iv centroid relative to that of Hβ, similar to earlier studies comparing C iv with Mg ii. The C iii] FWHM is found to correlate with the C iv FWHM, and hence is also poorly correlated with the Hβ FWHM. While the C iv and C iii] lines can be calibrated to yield consistent virial mass estimates as Hβ on average, the scatter is substantially larger than Mg ii, and the usage of C iv/C iii] FWHM in the mass estimators does not improve the agreement with the Hβ estimator. We discuss controversial claims in the literature on the correlation between C iv and Hβ FWHMs, and suggest that the reported correlation is either a result based on small samples or only valid for low-luminosity objects.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d82407cf09bb72d7d6236d502e7a94bed279abc5

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Citations in the corpus

A ∼50,000 M⊙ SOLAR MASS BLACK HOLE IN THE NUCLEUS OF RGG 118 (2015, background): “…has an associated scatter which contributes towards an uncertainty in the BH mass. Additionally, the scatter in the MBH − σ∗ relation (& 0.3 dex; Shen & Liu 2012) also contributes to the total uncertainty, since the dimensionless scale factor is determined by calibrating the ensemble of…”
Black Hole Growth to z = 2 - I: Improved Virial Methods for Measuring M_BH and L/L_Edd (2012, methodology): “The study of Shen & Liu (2012) presented a new sample of 60 luminous SDSS AGN atz ∼ 1.5−2.2, for which the CIV , Mg II , Hβ and Hα lines were measured, using high quality NIR spectroscopy.”
The Sloan Digital Sky Survey Reverberation Mapping Project: Sample Characterization (2018, methodology): “To measure the continuum and line fluxes from the spectra, we use a spectral fitting approach similar to our earlier work (e.g., Shen et al. 2008b, 2011; Shen & Liu 2012) but with a number of modifications, which we describe in detail below.”
THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: TECHNICAL OVERVIEW (2014, methodology): “…reliable detection of an Mg ii lag in NGC 4151 (Metzroth et al. 2006), and two marginal Mg ii lag detections in NGC 5548 (Clavel et al. 1991) and in NGC 3783 (Reichert et al. 1994), despite the fact that Mg ii shares many similarities with the Balmer lines (e.g., Shen et al. 2008; Shen & Liu 2012).”
THE FINAL SDSS HIGH-REDSHIFT QUASAR SAMPLE OF 52 QUASARS AT z > 5.7 (2016, methodology): “Using the near-IR spectrum in Figure 3, we estimate its central black hole mass based on the empirical scaling relations (Shen & Liu 2012).”