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

Abstract

<jats:title>Abstract</jats:title> <jats:p>We 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:sc>iv</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:sc>iv</jats:sc> parameter space measures of C <jats:sc>iv</jats:sc> EQW and blueshift, we define a “C <jats:sc>iv</jats:sc> ∥ distance” along a best-fit polynomial curve that incorporates information from both C <jats:sc>iv</jats:sc> parameters. We find that the C <jats:sc>iv</jats:sc> ∥ distance is linearly correlated with both the optical-to-X-ray slope, <jats:italic>α</jats:italic> <jats:sub>ox</jats:sub>, and broad-line He <jats:sc>ii</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:sc>iv</jats:sc> ∥ distance may be a better indicator of the mass-weighted accretion rate, parameterized by <jats:italic>L</jats:italic>/<jats:italic>L</jats:italic> <jats:sub>Edd</jats:sub>, than the C <jats:sc>iv</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:italic>L</jats:italic>/<jats:italic>L</jats:italic> <jats:sub>Edd</jats:sub> indicator. We find no X-ray or optical trends in the direction perpendicular to the C <jats:sc>iv</jats:sc> distance that could be used to reveal differences in accretion disk, wind, or corona structure that could be widening the C <jats:sc>iv</jats:sc> EQW–blueshift distribution. A different parameter (such as metallicity) not traced by these data must come into play.</jats:p>