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Correcting CIV-based virial black hole masses

Correcting CIV-based virial black hole masses
Correcting CIV-based virial black hole masses
The CIV broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV 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 CIV velocity-widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (log $L_{\rm Bol}$ = 45.5-48 erg/s), redshift 1.55000 km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24 dex at low CIV blueshifts (~0 km/s) and just 0.10 dex at high blueshifts (~3000 km/s), compared to 0.40 dex before the correction. The correction depends only on the CIV line properties - i.e. full-width at half maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature.
astro-ph.GA
0035-8711
2120–2142
Coatman, Liam
a3dbc7d0-84cf-4f21-9fb1-a5d169b51a6d
Hewett, Paul C.
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Richards, Gordon T.
0192698b-f415-4a89-9ea5-cd5f74a87755
Hennawi, Joseph F.
39c6c104-f4a2-4bbe-bdc9-f3eff7e91b84
Prochaska, J. Xavier
ae83475e-e500-47bb-bfe1-57986b01eeca
Coatman, Liam
a3dbc7d0-84cf-4f21-9fb1-a5d169b51a6d
Hewett, Paul C.
a4763f70-9f9a-4a4e-85ed-10694a66e5c9
Banerji, Manda
ce0a04bf-70a4-4b64-9027-b1a01def7325
Richards, Gordon T.
0192698b-f415-4a89-9ea5-cd5f74a87755
Hennawi, Joseph F.
39c6c104-f4a2-4bbe-bdc9-f3eff7e91b84
Prochaska, J. Xavier
ae83475e-e500-47bb-bfe1-57986b01eeca

Coatman, Liam, Hewett, Paul C., Banerji, Manda, Richards, Gordon T., Hennawi, Joseph F. and Prochaska, J. Xavier (2017) Correcting CIV-based virial black hole masses. Monthly Notices of the Royal Astronomical Society, 465 (2), 2120–2142. (doi:10.1093/mnras/stw2797).

Record type: Article

Abstract

The CIV broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV 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 CIV velocity-widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (log $L_{\rm Bol}$ = 45.5-48 erg/s), redshift 1.55000 km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24 dex at low CIV blueshifts (~0 km/s) and just 0.10 dex at high blueshifts (~3000 km/s), compared to 0.40 dex before the correction. The correction depends only on the CIV line properties - i.e. full-width at half maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature.

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Correcting C iv-Based Virial Black Hole Masses - Accepted Manuscript
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More information

Accepted/In Press date: 26 October 2016
e-pub ahead of print date: 30 October 2016
Published date: February 2017
Additional Information: Accepted for publication in MNRAS; fixed typo in CIV wavelength ARXIV IS AM
Keywords: astro-ph.GA

Identifiers

Local EPrints ID: 443894
URI: http://eprints.soton.ac.uk/id/eprint/443894
ISSN: 0035-8711
PURE UUID: f0e71038-9876-450a-a015-a91b487ebd5f

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Date deposited: 16 Sep 2020 16:34
Last modified: 25 Nov 2021 21:37

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Contributors

Author: Liam Coatman
Author: Paul C. Hewett
Author: Manda Banerji
Author: Gordon T. Richards
Author: Joseph F. Hennawi
Author: J. Xavier Prochaska

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