Structure and kinematics within the Starburst nucleus of M82: Searching for a bar

The structure and kinematics of the ionized gas within the starburst nucleus of M82 are investigated through high spectral (30 km s^-1^) and spatial (2") resolution observations of the 12.8 micron line of [Ne II]. The structure is dominated by a nuclear ring and two ionized "lanes." These components are found in other barred galaxies, supporting the suggestion that M82 may contain a nuclear bar. The ionized ring is approximately circular with a radius of 86 pc and an inclination of 73^deg^. The center of the ring closely corresponds to M82's kinematic center and is located at 9^h^51^m^43.4^s^ +/- 0.5", +69^deg^55'00.1"+/- 0.5" (1950). M82's systemic velocity is determined to be 200 +/- 7 km s^- 1^. The rotation curve becomes flat, with a terminal velocity of 112+/-5 km s^-1^ beyond 5" from the center. There are signs of outflow along the minor axis with a velocity ~55 km s^-1^. M82's rotation curve is searched for signs of the x, and x_2_ orbital families which make up a nuclear bar. Unfortunately, the orientation of M82's proposed bar is such that the expected rotation curves from barred or circular orbits are very similar. Hints of x, and x_2_ orbits are found in M82, but kinematic identification of a bar remains elusive. Observations of [Ar III] (8.99 microns), [S IV] (10.51 microns), and hydrogen Brα measure a lower level of excitation than that found in most Galactic H II regions, and which remains fairly constant across the galaxy. The total neon abundance is 1-2 times solar. The temperature of the stars ionizing the starburst regions is approximately 33,000 K. The Brα flux requires about 6 x 10^53^ Lyman continuum photons per second. Star formation has occurred either during a very brief burst (or bursts) or with an initial mass function with an upper mass cutoff approximately 25 M_sun_.