The morphology of the ionized gas in M31's bulge

This paper presents H-alpha + forbidden N II and B - 6200 A images of M31's bulge, made by coadding hundreds of CCD frames taken over the past five years. Exceptional detail is seen in the images; among the most interesting features are an inner region of gas which appears more face-on than M31's optical disk, an almost circular arm of emission curving around the southern half of the bulge, and a series of emission threads extending over 500 pc in length. New CCD spectroscopy of the forbidden S II lines 6716 and 6731 A reveals that the gas density falls off by at least two orders of magnitude in the central arcminute of the Galaxy. These data, the observed gas kinematics, and the lack of a sizable ISM in M31's bulge argue strongly for the existence of a galactic wind in this reigon. (Author)