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Black Hole Mass Estimates Based on C IV are Consistent With Those Based on the Balmer Lines

Assef, R. J. and Madsen, K. K. (2011) Black Hole Mass Estimates Based on C IV are Consistent With Those Based on the Balmer Lines. Astrophysical Journal, 742 (2). Art. No. 93. ISSN 0004-637X. doi:10.1088/0004-637X/742/2/93.

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Using a sample of high-redshift lensed quasars from the CASTLES project with observed-frame ultraviolet or optical and near-infrared spectra, we have searched for possible biases between supermassive black hole (BH) mass estimates based on the C IV, Hα, and Hβ broad emission lines. Our sample is based upon that of Greene, Peng, & Ludwig, expanded with new near-IR spectroscopic observations, consistently analyzed high signal-to-noise ratio (S/N) optical spectra, and consistent continuum luminosity estimates at 5100 Å. We find that BH mass estimates based on the full width at half-maximum (FWHM) of C IV show a systematic offset with respect to those obtained from the line dispersion, σ_l , of the same emission line, but not with those obtained from the FWHM of Hα and Hβ. The magnitude of the offset depends on the treatment of the He II and Fe II emission blended with C IV, but there is little scatter for any fixed measurement prescription. While we otherwise find no systematic offsets between C IV and Balmer line mass estimates, we do find that the residuals between them are strongly correlated with the ratio of the UV and optical continuum luminosities. This means that much of the dispersion in previous comparisons of C IV and Hβ BH mass estimates are due to the continuum luminosities rather than to any properties of the lines. Removing this dependency reduces the scatter between the UV- and optical-based BH mass estimates by a factor of approximately two, from roughly 0.35 to 0.18 dex. The dispersion is smallest when comparing the C IV σ l mass estimate, after removing the offset from the FWHM estimates, and either Balmer line mass estimate. The correlation with the continuum slope is likely due to a combination of reddening, host contamination, and object-dependent SED shapes. When we add additional heterogeneous measurements from the literature, the results are unchanged. Moreover, in a trial observation of a remaining outlier, the origin of the deviation is clearly due to unrecognized absorption in a low S/N spectrum. This not only highlights the importance of the quality of the observations, but also raises the question whether cases like this one are common in the literature, further biasing comparisons between C IV and other broad emission lines.

Item Type:Article
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URLURL TypeDescription
Assef, R. J.0000-0002-9508-3667
Madsen, K. K.0000-0003-1252-4891
Additional Information:© 2011 The American Astronomical Society. Received 2010 September 6; accepted 2011 August 30; published 2011 November 9. This work relies partly on observations of the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The Ohio State University; The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia. We thank Jenny E. Greene, Christopher Onken, Chien Y. Peng, Kristen Sellgren, Marianne Vestergaard, and Linda Watson for their help and suggestions that improved our work. We thank F. Courbin, E. Mediavilla, V. Motta, L. J. Goicoechea, S. Sluse, J. L. Tonry, L. Wisotzki, and J. Muñoz for sending us their optical spectra of Q2237+030, SDSS1138+0314, Q0957+561, HE1104−1805, B1422+231, and SBS0909+532. We thank F. Harrison for helping us obtain an optical spectrum of SDSS1151+0340.We also thank all the people in the LUCIFER science demonstration time team who did not participate directly in this work. We thank the anonymous referee for suggestions that helped improve our work. R.J.A. was supported in part by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. C.S.K. is supported by NSF grants AST-0708082 and AST-1009756. B.M.P., M.D., and R.W.P. are supported by NSF grant AST-1008882. P.M. is supported by NSF grant AST-0705170. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Space Radiation Laboratory, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:galaxies: active; gravitational lensing: strong; quasars: emission lines
Issue or Number:2
Record Number:CaltechAUTHORS:20111223-113541461
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Official Citation:Black Hole Mass Estimates Based on C IV are Consistent with Those Based on the Balmer Lines R. J. Assef et al. 2011 ApJ 742 93
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28591
Deposited On:03 Jan 2012 16:30
Last Modified:09 Nov 2021 16:58

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