MOJAVE. XVII. Jet Kinematics and Parent Population Properties of
  Relativistically Beamed Radio-Loud Blazars
  We present results from a parsec-scale jet kinematics study of 409 bright
radio-loud AGNs based on 15 GHz VLBA data obtained between 1994 August 31 and
2016 December 26 as part of the 2cm VLBA survey and MOJAVE programs. We tracked
1744 individual bright features in 382 jets over at least five epochs. A
majority (59%) of the best-sampled jet features showed evidence of accelerated
motion at the >3sigma level. Although most features within a jet typically have
speeds within ~40% of a characteristic median value, we identified 55 features
in 42 jets that had unusually slow pattern speeds, nearly all of which lie
within 4 pc (100 pc de-projected) of the core feature. Our results combined
with other speeds from the literature indicate a strong correlation between
apparent jet speed and synchrotron peak frequency, with the highest jet speeds
being found only in low-peaked AGNs. Using Monte Carlo simulations, we find
best fit parent population parameters for a complete sample of 174 quasars
above 1.5 Jy at 15 GHz. Acceptable fits are found with a jet population that
has a simple unbeamed power law luminosity function incorporating pure
luminosity evolution, and a power law Lorentz factor distribution ranging from
1.25 to 50 with slope -1.4 +- 0.2. The parent jets of the brightest radio
quasars have a space density of 261 +- 19 Gpc$^{-3}$ and unbeamed 15 GHz
luminosities above ~$10^{24.5}$ W/Hz, consistent with FR II class radio
galaxies.
