The orientation dependence of quasar single-epoch black hole mass
  scaling relationships
  Black hole masses are estimated for radio-loud quasars using several
self-consistent scaling relationships based on emission-line widths and
continuum luminosities. The emission lines used, H-beta, Mg II, and C IV, have
different dependencies on orientation as estimated by radio core dominance. We
compare differences in the log of black hole masses estimated from different
emission lines and show that they depend on radio core dominance in the sense
that core-dominated, jet-on objects have systematically smaller H-beta and Mg
II determined masses compared to those from C IV, while lobe-dominated edge-on
objects have systematically larger H-beta and Mg II determined masses compared
to those from C IV. The effect is consistent with the H-beta line width, and to
a lesser extent that of Mg II, being dependent upon orientation in the sense of
a axisymmetric velocity field plus a projection effect. The size of the effect
is nearly an order of magnitude in black hole mass going from one extreme
orientation to the other. We find that radio spectral index is a good proxy for
radio core dominance and repeating this analysis with radio spectral index
yields similar results. Accounting for orientation could in principle
significantly reduce the scatter in black hole mass scaling relationships, and
we quantify and offer a correction for this effect cast in terms of radio core
dominance and radio spectral index.
