3-DIMENSIONAL HYDRODYNAMIC SIMULATIONS OF NARROW-ANGLE-TAIL RADIO-SOURCES .1. THE BEGELMAN, REES, AND BLANDFORD MODEL

Narrow-angle-tail radio sources have been explained by various authors as being the result of ram-pressure-induced bending of supersonic radio jets by a transonic crosswind. The details of the models differ, but their common element is the necessity of a supersonic jet and a crosswind. We have, therefore, made a computational study of the bending of light supersonic jets by a wind flowing normally to it using the highly accurate RIEMANN code run at the highest resolutions that are currently feasible. RIEMANN is a three-dimensional hydrocode that implements the piecewise parabolic method of Colella and Woodward. An attempt is made to identify those characteristics of narrow-angle-tail sources that might have reasonably general physical explanations and then to verify whether these characteristics can be reproduced by simulations. In this work we have resolved the internal structure of the jet including primary and secondary oblique shocks. We have elucidated their role in jet bending and deceleration and the formation of knots. We have shown the effect of Rayleigh-Taylor instabilities on jet cross-sectional evolution. We have also resolved the Kelvin-Helmholtz instability through which the jet eventually disrupts. Our interpretations of the numerical results are supported with quantitative analyses whenever possible. We have also made detailed comparisons with the analytical work of Begelman, Rees, & Blandford. Moreover, we have applied our results to the interpretation of the archetypal narrow-angle-tail radio source NGC 1265.