Black hole mass estimates in quasars: A comparative analysis of high- and low-ionization lines

Context . The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (BLR), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars....

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Published in:Astronomy and astrophysics (Berlin) 2019-07, Vol.627, p.A88
Main Authors: Marziani, P., del Olmo, A., Martínez-Carballo, M. A., Martínez-Aldama, M. L., Stirpe, G. M., Negrete, C. A., Dultzin, D., D’Onofrio, M., Bon, E., Bon, N.
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Language:English
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Summary:Context . The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (BLR), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. Aims . We carried out an analysis of the C  IV λ 1549 and H β line profiles of 28 Hamburg-ESO high-luminosity quasars and of 48 low- z , low-luminosity sources in order to test whether the width of the high-ionization line C  IV λ 1549 could be correlated with H β and be used as a virial broadening estimator. Methods . We analyze intermediate- to high-S/N, moderate-resolution optical and near-infrared (NIR) spectra covering the redshifted C  IV λ 1549 and H β over a broad range of luminosity log L  ∼ 44 − 48.5 [erg s −1 ] and redshift (0 − 3), following an approach based on the quasar main sequence. Results . The present analysis indicates that the line width of C  IV λ 1549 is not immediately offering a virial broadening estimator equivalent to H β . At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(C  IV λ 1549) for Eddington ratio (using the C  IV λ 1549 blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Conclusions . Great care should be used in estimating high- L black hole masses M BH from C  IV λ 1549 line width. However, once a corrected FWHM C  IV λ 1549 is used, a C  IV λ 1549-based scaling law can yield unbiased M BH values with respect to the ones based on H β with sample standard deviation ≈0.3 dex.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201935265