3-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC JETS INJECTED ALONG A MAGNETIC-FIELD

We present the first numerical simulations of moderately hot, superson ic jets propagating initially along the field lines of a denser magnet ized background medium with Lorentz factor W = 4.56 and evolving in a four-dimensional spacetime. Compared with previous simulations in two spatial dimensions, the resulting structure and kinematics differ noti ceably: the density of the Mach disk is lower, and the head speed is s maller. This is because the impacted ambient fluid and its embedded ma gnetic field make efficient use of the third spatial dimension as they are deflected circularly off of the head of the jet. As a result, a s ignificant magnetic field component normal to the jet is created near the head. If the field is strong, backflow and field reversals are str ongly suppressed; upstream, the field closes back on the surface of th e beam and assists the collimation of the jet. If the field is weak, b ackflow and field reversals are more pronounced, although still not as extended as in the corresponding plane-parallel case. In all studied cases, the high-pressure region is localized near the jet head irrespe ctive of the presence/strength of the magnetic field, and the head dec elerates efficiently by transferring momentum to the background fluid that recedes along a thin bow shock in all directions. Furthermore, tw o oppositely directed currents circle near the surface of the cylindri cal beam, and a third current circles on the bow shock. These prelimin ary results underline the importance of performing fully three-dimensi onal simulations to investigate the morphology and propagation of rela tivistic extragalactic jets.