NOEMA High-fidelity Imaging of the Molecular Gas in and around M82

Abstract

We present a 154 pointing IRAM NOEMA mosaic of the CO(1–0) line emission in and around the nearby starburst galaxy M82. The observations, complemented by zero-spacing observations, reach a spatial resolution of ∼30 pc (∼1.″9) at 5.0 km s −1 spectral resolution, sufficient to resolve the molecular gas in the central starburst disk, the outflow, and the tidal streamers. The resulting moment and peak brightness maps show a striking amount of structure. Using a clump decomposition algorithm, we analyze the physical properties (e.g., radii R , line widths σ , and masses M ) of ∼2000 molecular clouds. To first order, the clouds’ properties are very similar, irrespective of their environment. This also holds for the size–line width relations of the clouds. The distribution of clouds in the σ 2 / R versus column density Σ space suggests that external pressure does not play a significant role in setting their physical parameters in the outflow and streamers. We find that the clouds in the streamers stay approximately constant in size ( R ∼ 50 pc) and mass ( M ∼ 10 5 M ⊙ ) and do not vary with their projected distance from M82's center. The clouds in the outflow, on the other hand, appear to decrease in size and mass with distance toward the southern outflow. The reduction in the molecular gas luminosity could be indicative of cloud evaporation of embedded clouds in the hot outflow.