Does Size Matter? The Underlying Intrinsic Size Distribution of Radio
  Sources and Implications for Unification by Orientation
  Unification by orientation is a ubiquitous concept in the study of active
galactic nuclei. A gold standard of the orientation paradigm is the hypothesis
that radio galaxies and radio-loud quasars are intrinsically the same, but are
observed over different ranges of viewing angles. Historically, strong support
for this model was provided by the projected sizes of radio structure in
luminous radio galaxies, which were found to be significantly larger than those
of quasars, as predicted due to simple geometric projection. Recently, this
test of the simplest prediction of orientation-based models has been revisited
with larger samples that cover wider ranges of fundamental properties---and no
clear difference in projected sizes of radio structure is found. Cast solely in
terms of viewing angle effects, these results provide convincing evidence that
unification of these objects solely through orientation fails. However, it is
possible that conflicting results regarding the role orientation plays in our
view of radio sources simply result from insufficient sampling of their
intrinsic size distribution. We test this possibility using Monte-Carlo
simulations constrained by real sample sizes and properties. We develop models
for the real intrinsic size distribution of radio sources, simulate
observations by randomly sampling intrinsic sizes and viewing angles, and
analyze how likely each sample is to support or dispute unification by
orientation. We find that, while it is possible to reconcile conflicting
results purely within a simple, orientation-based framework, it is very
unlikely. We analyze the effects that sample size, relative numbers of radio
galaxies and quasars, the critical angle that separates the two subclasses, and
the shape of the intrinsic size distribution have on this type of test.
