Molecular Gas in M82: Resolving the Outflow and Streamers

We present a high–resolution (3.6, 70 pc) CO(J = 1 → 0) mosaic of the molecular gas in M82 covering an area of 2.5×3.5 (2.8 kpc×3.9 kpc) 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 × 10 M⊙) 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 M82. This provides evidence that the molecular gas within M82’s optical disk is disrupted by the interaction with M81. Molecular gas is found in M82’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 ∼ 230km s; we derive an opening angle of ∼ 55 for the molecular outflow cone. The total amount of gas in the outflow is > 3× 10 M⊙ and its kinetic energy is of order 10 55 erg, about one percent of the estimated total mechanical energy input of M82’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). Subject headings: galaxies:individual (M 82)–galaxies: interactions–galaxies: kinematics and dynamics–galaxies:ISM–galaxies: starburst–ISM: jets and outflows