3D Hydrodynamic Simulations of Relativistic Extragalactic Jets

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Abstract
We describe a new numerical 3D relativistic hydrodynamical code, the results of validation tests, and a comparison with earlier, 2D studies. The 3D code has been used to study the deflection and precession of relativistic flows. We find that even quite fast jets (gamma~10) can be significantly influenced by impinging on an oblique density gradient, exhibiting a rotation of the Mach disk in the jet's head. The flow is bent via a potentially strong, oblique internal shock that arises due to asymmetric perturbation of the flow by its cocoon. In extreme cases this cocoon can form a marginally relativistic flow orthogonal to the jet, leading to large scale dynamics quite unlike that normally associated with astrophysical jets. Exploration of a gamma=5 flow subject to a large amplitude precession (semi-angle 11.25dg) shows that it retains its integrity, with modest reduction in Lorentz factor and momentum flux, for almost 50 jet-radii, but thereafter, the collimated flow is disrupted. The flow is approximately ballistic, with velocity vectors not aligned with the local jet `wall'. We consider simple estimators of the flow emissivity in each case and conclude that a) while the oblique internal shocks which mediate a small change in the direction of the deflected flows have little impact on the global dynamics, significantly enhanced flow emission (by a factor of 2-3) may be associated with such regions; and b) the convolution of rest frame emissivity and Doppler boost in the case of the precessed jet invariably leads to a core-jet-like structure, but that intensity fluctuations in the jet cannot be uniquely associated with either change in internal conditions or Doppler boost alone, but in general are a combination of both factors.

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