Molecular Gas in M82: Resolving the Outflow and Streamers

We present a high-resolution (36, 70 pc) ¹²CO (J = 1 → 0) mosaic of the molecular gas in M82 covering an area of 25 × 35 (2.8 × 3.9 kpc) obtained with the Owens Valley Radio Observatory millimeter interferometer. The observations reveal the presence of huge amounts of molecular gas (>70% of the total molecular mass, M_tot ≈ 1.3 × 10⁹ 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 H I 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 ~230 km s^-1; we derive an opening angle of ~55° for the molecular outflow cone. The total amount of gas in the outflow is greater than 3 × 10⁸ M_☉, and its kinetic energy is of order 10⁵⁵ ergs, about 1% 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 into a galaxy's halo (and even to the intergalactic medium).