Comparing different indicators of quasar orientation
  Radio core dominance, the rest-frame ratio of core to lobe luminosity, has
been widely used as a measure of Doppler boosting of a quasar's radio jets and
hence of the inclination of the central engine's spin axis to the line of
sight. However, the use of the radio lobe luminosity in the denominator
(essentially to try and factor out the intrinsic power of the central engine)
has been criticized and other proxies for the intrinsic engine power have been
proposed. These include the optical continuum luminosity, and the luminosity of
the narrow-line region. Each is plausible, but so far none has been shown to be
clearly better than the others. In this paper we evaluate four different
measures of core dominance using a new sample of 126 radio loud quasars,
carefully selected to be as free as possible of orientation bias, together with
high quality VLA images and optical spectra from the SDSS. We find that
normalizing the radio core luminosity by the optical continuum luminosity
yields a demonstrably superior orientation indicator. In addition, by comparing
the equivalent widths of broad emission lines in our orientation-unbiased
sample to those of sources in the MOJAVE program, we show that the beamed
optical synchrotron emission from the jets is not a significant component of
the optical continuum for the sources in our sample. We also discuss future
applications of these results.
