The Sloan Digital Sky Survey Reverberation Mapping Project: Low-Ionization Broad-Line Widths and Implications for Virial Black Hole Mass Estimation. (arXiv:1903.10015v1 [astro-ph.GA])

The Sloan Digital Sky Survey Reverberation Mapping Project: Low-Ionization Broad-Line Widths and Implications for Virial Black Hole Mass Estimation. (arXiv:1903.10015v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wang_S/0/1/0/all/0/1">Shu Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shen_Y/0/1/0/all/0/1">Yue Shen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jiang_L/0/1/0/all/0/1">Linhua Jiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Horne_K/0/1/0/all/0/1">Keith Horne</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_W/0/1/0/all/0/1">W. N. Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Grier_C/0/1/0/all/0/1">C. J. Grier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ho_L/0/1/0/all/0/1">Luis C. Ho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Homayouni_Y/0/1/0/all/0/1">Yasaman Homayouni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_J/0/1/0/all/0/1">Jennifer I-Hsiu Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneider_D/0/1/0/all/0/1">Donald P. Schneider</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Trump_J/0/1/0/all/0/1">Jonathan R. Trump</a>

The width of the broad emission lines in quasars is commonly characterized
either by the full-width-at-half-maximum (FWHM) or the square root of the
second moment of the line profile ($sigma_{rm line}$), and used as an
indicator of the virial velocity of the broad-line region (BLR) in the
estimation of black hole (BH) mass. We measure FWHM and $sigma_{rm line}$ for
H$alpha$, H$beta$ and Mg II broad lines in both the mean and root-mean-square
(rms) spectra of a large sample of quasars from the Sloan Digital Sky Survey
Reverberation Mapping (SDSS-RM) project. We introduce a new quantitative recipe
to measure $sigma_{rm line}$ that is reproducible, less susceptible to noise
and blending in the wings, and scales with the intrinsic width of the line. We
compare the four definitions of line width (FWHM and $sigma_{rm line}$ in
mean and rms spectra, respectively) for each of the three broad lines and among
different lines. There are strong correlations among different width
definitions for each line, as well as correlations among different lines. We
further investigate the correlations between virial BH masses using different
line width definitions and the stellar velocity dispersion of the host
galaxies, and the dependence of line shape (characterized by the ratio
FWHM/$sigma_{rm line}$) on physical properties of the quasar. Our results
provide further evidence that FWHM is more sensitive to the orientation of a
flattened BLR geometry than $sigma_{rm line}$, but the overall comparison
between the virial BH mass and host stellar velocity dispersion does not
provide conclusive evidence that one particular width definition is
significantly better than the others.

The width of the broad emission lines in quasars is commonly characterized
either by the full-width-at-half-maximum (FWHM) or the square root of the
second moment of the line profile ($sigma_{rm line}$), and used as an
indicator of the virial velocity of the broad-line region (BLR) in the
estimation of black hole (BH) mass. We measure FWHM and $sigma_{rm line}$ for
H$alpha$, H$beta$ and Mg II broad lines in both the mean and root-mean-square
(rms) spectra of a large sample of quasars from the Sloan Digital Sky Survey
Reverberation Mapping (SDSS-RM) project. We introduce a new quantitative recipe
to measure $sigma_{rm line}$ that is reproducible, less susceptible to noise
and blending in the wings, and scales with the intrinsic width of the line. We
compare the four definitions of line width (FWHM and $sigma_{rm line}$ in
mean and rms spectra, respectively) for each of the three broad lines and among
different lines. There are strong correlations among different width
definitions for each line, as well as correlations among different lines. We
further investigate the correlations between virial BH masses using different
line width definitions and the stellar velocity dispersion of the host
galaxies, and the dependence of line shape (characterized by the ratio
FWHM/$sigma_{rm line}$) on physical properties of the quasar. Our results
provide further evidence that FWHM is more sensitive to the orientation of a
flattened BLR geometry than $sigma_{rm line}$, but the overall comparison
between the virial BH mass and host stellar velocity dispersion does not
provide conclusive evidence that one particular width definition is
significantly better than the others.

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