Molecular Gas in M82: Resolving the Outflow and Streamers

We present a high-resolution (3. 6'', 70pc) CO (1-0) mosaic of the molecular gas in M 82 covering an area of 2. 5' x 3. 5' (2. 8kpc x 3. 9kpc) obtained with the OVRO millimeter interferometer. The observations reveal the presence of huge amounts of molecular gas (> 70% of the total molecular mass, Mₜot=1. 3 x 10⁹ Mₛun) outside the central 1 kpc disk. Molecular streamers are detected in and below M82's disk out to distances from the center of 1. 7 kpc. Some of these streamers are well correlated with optical absorption features; they form the basis of some of the prominent tidal HI features around M 82. This provides evidence that the molecular gas within M 82's optical disk is disrupted by the interaction with M 81. Molecular gas is found in M 82's outflow/halo, reaching distances up to 1. 2 kpc below the plane; CO line-splitting has been detected for the first time in the outflow. The maximum outflow velocity is 230 km/s; we derive an opening angle of 55 deg for the molecular outflow cone. The total amount of gas in the outflow is >3 x 10⁸ Mₛun and its kinetic energy is of order 10⁵5 erg, about one percent of the estimated total mechanical energy input of M 82's starburst. Our study implies that extreme starburst environments can move significant amounts of molecular gas in to a galaxy's halo (and even to the intergalactic medium).