MOJAVE XIII. Parsec-Scale AGN Jet Kinematics Analysis Based on 19 years
  of VLBA Observations at 15 GHz
  We present 1625 new 15 GHz (2 cm) VLBA images of 295 jets associated with
active galactic nuclei (AGNs) from the MOJAVE and 2 cm VLBA surveys, spanning
observations between 1994 Aug 31 and 2013 Aug 20. For 274 AGNs with at least 5
VLBA epochs, we have analyzed the kinematics of 961 individual bright features
in their parsec-scale jets. A total of 122 of these jets have not been
previously analyzed by the MOJAVE program. In the case of 451 jet features that
had at least 10 epochs, we also examined their kinematics for possible
accelerations. At least half of the well-sampled features have non-radial
and/or accelerating trajectories, indicating that non-ballistic motion is
common in AGN jets. Since it is impossible to extrapolate any accelerations
that occurred before our monitoring period, we could only determine reliable
ejection dates for about 24% of those features that had significant proper
motions. The distribution of maximum apparent jet speeds in all 295 AGNs
measured by our program to date is peaked below 5c, with very few jets with
apparent speeds above 30c. The fastest speed in our survey is about 50c,
measured in the jet of the quasar PKS 0805-07, and is indicative of a maximum
jet Lorentz factor of about 50 in the parent population. The Fermi LAT-detected
gamma-ray AGNs in our sample have, on average, higher jet speeds than non
LAT-detected AGNs, indicating a strong correlation between pc-scale jet speed
and gamma-ray Doppler boosting factor. We have identified 11 moderate-redshift
(z<0.35) AGNs with fast apparent speeds (>10c) that are strong candidates for
future TeV gamma-ray detection. Of the five gamma-ray loud narrow-lined Seyfert
I AGNs in our sample, three show highly superluminal jet motions, while the
others have sub-luminal speeds. (abridged)
