The Asymmetric Wind in M82

We have obtained detailed imaging Fabry-Perot observations of the nearbygalaxy M82, in order to understand the physical association between thehigh-velocity outflow and the starburst nucleus. The observed velocities of theemitting gas in M82 reveal a bipolar outflow of material, originating from thebright starburst regions in the galaxy's inner disk, but misaligned withrespect to the galaxy spin axis. The deprojected outflow velocity increaseswith radius from 525 to 655 km/s. Spectral lines show double components in thecenters of the outflowing lobes, with the H-alpha line split by ~300 km/s overa region almost a kiloparsec in size. The filaments are not simple surfaces ofrevolution, nor is the emission distributed evenly over the surfaces. We modelthese lobes as a composite of cylindrical and conical structures, collimated inthe inner ~500 pc but expanding at a larger opening angle of ~25 degrees beyondthat radius. We compare our kinematic model with simulations ofstarburst-driven winds in which disk material surrounding the source isentrained by the wind. The data also reveal a remarkably low [NII]/H-alpharatio in the region of the outflow, indicating that photoionization by thenuclear starburst may play a significant role in the excitation of the opticalfilament gas, particularly near the nucleus.Comment: 42 pages AASTeX with 16 figures; accepted for publication in ApJ; figures reformatted for better printin