Hydrodynamical Simulations of Colliding Jets
  Radio observations suggest that 3C 75, located in the dumbbell shaped galaxy
NGC 1128 at the center of Abell 400, hosts two colliding jets. Motivated by
this source, we perform three-dimensional hydrodynamical simulations using a
modified version of the GPU-accelerated Adaptive-MEsh-Refinement hydrodynamical
parallel code ($\mathit{GAMER}$) to study colliding extragalactic jets. We find
that colliding jets can be cast into two categories: 1) bouncing jets, in which
case the jets bounce off each other keeping their identities, and 2) merging
jets, when only one jet emerges from the collision. Under some conditions the
interaction causes the jets to break up into oscillating filaments of opposite
helicity, with consequences for their downstream stability. When one jet is
significantly faster than the other and the impact parameter is small, the jets
merge; the faster jet takes over the slower one. In the case of merging jets,
the oscillations of the filaments, in projection, may show a feature which
resembles a double helix, similar to the radio image of 3C 75. Thus we
interpret the morphology of 3C 75 as a consequence of the collision of two jets
with distinctly different speeds at a small impact parameter, with the faster
jet breaking up into two oscillating filaments.
