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Exploring Changes in Quasar Spectral Energy Distributions across C iv Parameter Space

Published version
Peer-reviewed

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Abstract

jats:titleAbstract</jats:title> jats:pWe examine the UV/X-ray properties of 1378 quasars in order to link empirical correlations to theoretical models of the physical mechanisms dominating quasars as a function of mass and accretion rate. The clarity of these correlations is improved when (1) using C jats:sciv</jats:sc> broad emission line equivalent width (EQW) and blueshift (relative to systemic) values calculated from high signal-to-noise ratio reconstructions of optical/UV spectra and (2) removing quasars expected to be absorbed based on their UV/X-ray spectral slopes. In addition to using the traditional C jats:sciv</jats:sc> parameter space measures of C jats:sciv</jats:sc> EQW and blueshift, we define a “C jats:sciv</jats:sc> ∥ distance” along a best-fit polynomial curve that incorporates information from both C jats:sciv</jats:sc> parameters. We find that the C jats:sciv</jats:sc> ∥ distance is linearly correlated with both the optical-to-X-ray slope, jats:italicα</jats:italic> jats:subox</jats:sub>, and broad-line He jats:scii</jats:sc> EQW, which are known spectral energy distribution indicators, but does not require X-ray or high spectral resolution UV observations to compute. The C jats:sciv</jats:sc> ∥ distance may be a better indicator of the mass-weighted accretion rate, parameterized by jats:italicL</jats:italic>/jats:italicL</jats:italic> jats:subEdd</jats:sub>, than the C jats:sciv</jats:sc> EQW or blueshift alone, as those relationships are known to break down at the extrema. Conversely, there is only a weak correlation with the X-ray energy index (Γ), an alternate jats:italicL</jats:italic>/jats:italicL</jats:italic> jats:subEdd</jats:sub> indicator. We find no X-ray or optical trends in the direction perpendicular to the C jats:sciv</jats:sc> distance that could be used to reveal differences in accretion disk, wind, or corona structure that could be widening the C jats:sciv</jats:sc> EQW–blueshift distribution. A different parameter (such as metallicity) not traced by these data must come into play.</jats:p>

Description

Keywords

5101 Astronomical Sciences, 51 Physical Sciences

Journal Title

Astrophysical Journal

Conference Name

Journal ISSN

0004-637X
1538-4357

Volume Title

931

Publisher

American Astronomical Society
Sponsorship
National Aeronautics and Space Administration (NASA) (NAS5- 26555)
National Aeronautics and Space Administration (NASA) (G07-18110X)
NSF ∣ National Science Board (NSB) (1908716)