Molecular Bubbles and Outflows in the Edge-on Starburst Galaxies M82 and NGC 2146

We performed deep CO(1-0) mapping of the central 60′′ regions of nearby edge-on starburst galaxies M82 and NGC 2146 with the Nobeyama Millimeter Array. Both galaxies show kpc-scale Hα and/or soft X-ray outflows emanating from starburst regions within the galactic disks [1, 2]. We succeeded in imaging molecular bubbles and filamentary structures inside and outside the galactic disks in both galaxies. The mass and energy of the molecular bubbles show ∼ 1.8×10 M and ∼ (0.5−2)×10 ergs for M82 [3] and ∼ 1.5 × 10 M and ∼ (2 − 5) × 10 ergs for NGC 2146, respectively. The total thermal energies of Hα and X-ray outflows in M82 are ∼ 7× 10 ergs [1] and ∼ 4× 10 ergs [4], respectively, and that of X-ray outflows within the central 60′′ of NGC 2146 is ∼ 3×10 ergs [5], assuming the filling factor of the Hα and X-ray is 0.01. These results indicate that the energy of a molecular bubble almost corresponds to that of the whole Hα or X-ray outflows in a galaxy. Note that the energy of a HI bubble in other galaxies is much smaller, < 10 ergs [6]. Although our result is based only on two galaxies (but typical starburst galaxies), it suggests that the molecular gas is one of the dominant components of outflows in starburst galaxies in terms of the energetics.