Logo image
Back
Correcting C IV-based virial black hole masses
Journal article   Open access

Correcting C IV-based virial black hole masses

Liam Coatman, Paul C. Hewett, Manda Banerji, Gordon T. Richards, Joseph F. Hennawi and J. Xavier Prochaska
Monthly notices of the Royal Astronomical Society, v 465(2), pp 2120-2142
01 Feb 2017
DOI: https://doi.org/10.1093/mnras/stw2797
url
https://eprints.soton.ac.uk/443894/1/Correcting_C_iv_Based_Virial_Black_Hole_Masses.pdfView
Accepted (AM)Open Access (License Unspecified),  Open

Abstract

Astronomy & Astrophysics Physical Sciences Science & Technology
The C IV lambda lambda 1498,1501 broad emission line is visible in optical spectra to redshifts exceeding z similar to 5. C IV has long been known to exhibit significant displacements to the blue and these 'blueshifts' almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from C IV velocity widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (L-Bol = 10(45.5)-10(48) erg s(-1)), redshift 1.5 < z < 4.0 quasars with both C IV and Balmer line spectra, we have quantified the bias in C IV BH masses as a function of the C IV blueshift. C IV BH masses are shown to be a factor of 5 larger than the corresponding Balmer-line masses at C IV blueshifts of 3000 km s(-1) and are overestimated by almost an order of magnitude at the most extreme blueshifts, greater than or similar to 5000 km s(-1). Using the monotonically increasing relationship between the C IV blueshift and the mass ratio BH(C IV)/BH(H alpha), we derive an empirical correction to all C IV BH masses. The scatter between the corrected C IV masses and the Balmer masses is 0.24 dex at low C IV blueshifts (similar to 0 km s(-1)) and just 0.10 dex at high blueshifts (similar to 000 km s(-1)), compared to 0.40 dex before the correction. The correction depends only on the C IV line properties - i.e. full width at half-maximum and blueshift - and can therefore be applied to all quasars where C IV emission line properties have been measured, enabling the derivation of unbiased virial BH-mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature.

Metrics

10 Record Views
162 citations in Web of Science
149 citations in Scopus

Details

InCites Highlights

Data related to this publication, from InCites Benchmarking & Analytics tool:

Collaboration types
Domestic collaboration
International collaboration
Web of Science research areas
Astronomy & Astrophysics
Logo image