Session 77 - Irregular and Star Burst Galaxies.
Oral session, Thursday, June 11
Presidio,

## [77.03] H\alpha Emission 11 kpc Above M82

D. Devine (GSFC), J. Bally (U. Colorado)

We report the discovery of H\alpha emission extending out to a projected distance of 11 kpc from the disk of M82, which is three times farther than previously identified emission line components associated with the nuclear superwind. The H\alpha emission can be traced nearly continuously for ten arcminutes northwest of M82 out to an emission line structure (the cap''), which lies at a projected distance of 11 - 12 kpc from the M82 nucleus. The cap has a shell-like morphology and is blueshifted by 50 - 200 km s^-1 relative to the M82 nucleus. The cap'' may be photoionized material illuminated by Lyman continuum photons leaking out of the M82 nuclear region through the hot bipolar cavity produced by the starburst driven superwind, or it may be a bow shock formed by the impact of the superwind with either previously emitted wind material or with ambient intergalactic material and/or tidal debris left over from the collision between M81 and M82.