MOJAVE - XIV. Shapes and opening angles of AGN jets
  We present 15 GHz stacked VLBA images of 373 jets associated with active
galactic nuclei (AGN) having at least five observing epochs within a 20 yr time
interval 1994-2015 from the MOJAVE programme and/or its precursor, the 2 cm
VLBA Survey. These data are supplemented by 1.4 GHz single-epoch VLBA
observations of 135 MOJAVE AGNs to probe larger scale jet structures. The
typical jet geometry is found to be close to conical on scales from hundreds to
thousands of parsecs, while a number of galaxies show quasi-parabolic
streamlines on smaller scales. A true jet geometry in a considerable fraction
of AGNs appears only after stacking epochs over several years. The jets with
significant radial accelerated motion undergo more active collimation. We have
analysed total intensity jet profiles transverse to the local jet ridgeline and
derived both apparent and intrinsic opening angles of the flows, with medians
of $21.5\deg$ and $1.3\deg$, respectively. The Fermi LAT-detected gamma-ray
AGNs in our sample have, on average, wider apparent and narrower intrinsic
opening angle, and smaller viewing angle than non LAT-detected AGNs. We have
established a highly significant correlation between the apparent opening angle
and gamma-ray luminosity, driven by Doppler beaming and projection effects.
