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Title: DO QUASAR BROAD-LINE VELOCITY WIDTHS ADD ANY INFORMATION TO VIRIAL BLACK HOLE MASS ESTIMATES?

Abstract

We examine how much information measured broad-line widths add to virial black hole (BH) mass estimates for flux-limited samples of quasars. We do this by comparing the BH mass estimates to those derived by randomly reassigning the quasar broad-line widths to different objects and re-calculating the BH mass. For 9000 BH masses derived from the H{beta} line we find that the distributions of original and randomized BH masses in the M{sub BH}-redshift plane and the M{sub BH}-luminosity plane are formally identical. A two-dimensional Kolmogorov-Smirnov test does not find a difference at >90% confidence. For the Mg II line (32,000 quasars) we do find very significant differences between the randomized and original BH masses, but the amplitude of the difference is still small. The difference for the C IV line (14,000 quasars) is 2{sigma}-3{sigma} and again the amplitude of the difference is small. Subdividing the data into redshift and luminosity bins we find that the median absolute difference in BH mass between the original and randomized data is 0.025, 0.01, and 0.04 dex for H{beta}, Mg II, and C IV, respectively. The maximum absolute difference is always {<=}0.1 dex. We investigate whether our results are sensitive to corrections to Mg IImore » virial masses, such as those suggested by Onken and Kollmeier. These corrections do not influence our results, other than to reduce the significance of the difference between original and randomized BH masses to only 1{sigma}-2{sigma} for Mg II. Moreover, we demonstrate that the correlation between mass residuals and Eddington ratio discussed by Onken and Kollmeier is more directly attributable to the slope of the relation between H{beta} and Mg II line width. The implication is that the measured quasar broad-line velocity widths provide little extra information, after allowing for the mean velocity width. In this case virial estimates are equivalent to M{sub BH}{proportional_to}L{sup {alpha}}, with L/L{sub Edd}{proportional_to}L{sup 1-{alpha}} (with {alpha} {approx_equal} 0.5). This leaves an unanswered question of why the accretion efficiency changes with luminosity in just the right way to keep the mean broad-line widths fixed as a function of luminosity.« less

Authors:
 [1]
  1. Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia)
Publication Date:
OSTI Identifier:
21578230
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 736; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/736/2/161; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; EMISSION; GALAXIES; LINE WIDTHS; LUMINOSITY; MASS; QUASARS; RED SHIFT; VELOCITY; COSMIC RADIO SOURCES; OPTICAL PROPERTIES; PHYSICAL PROPERTIES

Citation Formats

Croom, Scott M., E-mail: scroom@physics.usyd.edu.au. DO QUASAR BROAD-LINE VELOCITY WIDTHS ADD ANY INFORMATION TO VIRIAL BLACK HOLE MASS ESTIMATES?. United States: N. p., 2011. Web. doi:10.1088/0004-637X/736/2/161.
Croom, Scott M., E-mail: scroom@physics.usyd.edu.au. DO QUASAR BROAD-LINE VELOCITY WIDTHS ADD ANY INFORMATION TO VIRIAL BLACK HOLE MASS ESTIMATES?. United States. doi:10.1088/0004-637X/736/2/161.
Croom, Scott M., E-mail: scroom@physics.usyd.edu.au. Mon . "DO QUASAR BROAD-LINE VELOCITY WIDTHS ADD ANY INFORMATION TO VIRIAL BLACK HOLE MASS ESTIMATES?". United States. doi:10.1088/0004-637X/736/2/161.
@article{osti_21578230,
title = {DO QUASAR BROAD-LINE VELOCITY WIDTHS ADD ANY INFORMATION TO VIRIAL BLACK HOLE MASS ESTIMATES?},
author = {Croom, Scott M., E-mail: scroom@physics.usyd.edu.au},
abstractNote = {We examine how much information measured broad-line widths add to virial black hole (BH) mass estimates for flux-limited samples of quasars. We do this by comparing the BH mass estimates to those derived by randomly reassigning the quasar broad-line widths to different objects and re-calculating the BH mass. For 9000 BH masses derived from the H{beta} line we find that the distributions of original and randomized BH masses in the M{sub BH}-redshift plane and the M{sub BH}-luminosity plane are formally identical. A two-dimensional Kolmogorov-Smirnov test does not find a difference at >90% confidence. For the Mg II line (32,000 quasars) we do find very significant differences between the randomized and original BH masses, but the amplitude of the difference is still small. The difference for the C IV line (14,000 quasars) is 2{sigma}-3{sigma} and again the amplitude of the difference is small. Subdividing the data into redshift and luminosity bins we find that the median absolute difference in BH mass between the original and randomized data is 0.025, 0.01, and 0.04 dex for H{beta}, Mg II, and C IV, respectively. The maximum absolute difference is always {<=}0.1 dex. We investigate whether our results are sensitive to corrections to Mg II virial masses, such as those suggested by Onken and Kollmeier. These corrections do not influence our results, other than to reduce the significance of the difference between original and randomized BH masses to only 1{sigma}-2{sigma} for Mg II. Moreover, we demonstrate that the correlation between mass residuals and Eddington ratio discussed by Onken and Kollmeier is more directly attributable to the slope of the relation between H{beta} and Mg II line width. The implication is that the measured quasar broad-line velocity widths provide little extra information, after allowing for the mean velocity width. In this case virial estimates are equivalent to M{sub BH}{proportional_to}L{sup {alpha}}, with L/L{sub Edd}{proportional_to}L{sup 1-{alpha}} (with {alpha} {approx_equal} 0.5). This leaves an unanswered question of why the accretion efficiency changes with luminosity in just the right way to keep the mean broad-line widths fixed as a function of luminosity.},
doi = {10.1088/0004-637X/736/2/161},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 736,
place = {United States},
year = {2011},
month = {8}
}