The Cone-Like H-alpha Nebula in NGC 4945: A Galactic Superwind Bow Shock ?

Abstract

We find that a non-axisymmetric bow shock model, with an appropriate choice of parameters, could fit the line splitting velocity field of the cone-like H$α$ nebula in NGC 4945 better than a canonical cone model. Meanwhile, the bow shock model could also reproduce the morphology of the H$α$ nebula. The bow shock results from the interaction of the galactic superwinds with a giant HII region. It is implied that the starburst ring or disk around the galactic nucleus should be generating strong winds, and the bright H$α$ knot northwest of the nucleus be suffering an anisotropic mass loss process.

14 pages, aasms4.sty, 3 figures not included (available upon request) To appear in ApJ Letters. email chy, jhh@crater.nju.edu.cn