THE ASYMMETRIC WIND IN M82

We have obtained detailed Fabry-Perot imaging observations of the near by galaxy M82 in order to understand the physical association between the high-velocity outflow and the starburst nucleus. The high spatial and kinematic resolution of our observations has allowed us to perform photometric analyses of H alpha, [N II], and [O III] spectral lines a t roughly 100,000 positions across the extent of the galaxy. The obser ved velocities of the emitting gas in M82 reveal a bipolar outflow of material, originating from the bright starburst regions in the galaxy' s inner disk but misaligned with respect to the galaxy spin axis. The deprojected out flow velocity indicated by the optical filaments incre ases with radius from 525 to 655 km s(-1). All three spectral lines sh ow double components in the centers of the outflowing lobes, with the H alpha line split by similar to 300 km s(-1) over a region almost 1 k pc in size. The filamentary lobes lie along an axis tilted by 15 degre es with respect to the spin axis, a finding confirmed by the regions o f line splitting and by the ionization pattern over the outflow. The f ilaments are not simple surfaces of revolution, nor is the emission di stributed evenly over the surfaces. We model these lobes as a composit e of cylindrical and conical structures, collimated in the inner simil ar to 500 pc but expanding at a larger opening angle of similar to 25 degrees beyond that radius. We compare our kinematic model with simula tions of starburst-driven winds in which disk material surrounding the source is entrained by the wind. There is some evidence for rotation of the wind filaments about the outflow axis in support of entrainment , and we find strong similarities between the observed and predicted s tructures. The data reveal a remarkably low [N II]/H alpha ratio in th e region of the outflow, indicating that photoionization by the nuclea r starburst may play a significant role in the excitation of the optic al filament gas, particularly near the nucleus. An increase in the [O III]/H alpha ratio along the outflow is observed. At larger radii, the line diagnostics and a strong spatial correlation between H alpha and soft X-ray filaments are consistent with shock ionization.A smooth sp herical halo around M82, extending to at least 2 kpc, is observed in e mission lines. We propose that the dusty halo is the primary source of the linearly polarized optical emission. A diffuse ionized medium wit h enhanced [N II]/H alpha emission pervades the stellar disk. We discu ss likely sources of ionization and heating.