Large-Field CO (J = 1→0) Observations of the Starburst Galaxy M 82

Abstract

Abstract We present large-field (15.7 $ \times$ 16.9 arcmin$ ^2$ ) CO ($ J$$ =$ 1$ \rightarrow$ 0) observations of the starburst galaxy M 82, at an angular resolution of 22$ ''$ with the NRO 45-m telescope. The CO emission was detected in the galactic disk, outflow (driven by the galactic wind) up to $ \sim$ 2 kpc above the galactic plane in the halo, and in tidal streams. The kinematics of the outflow (including CO line splitting) suggests that it has the shape of a cylinder that is diverging outwards. The mass and kinetic energy of the molecular gas outflow are estimated to be (0.26–1.0) $ \times$ 10$ ^{9}\ M_{\odot}$ and (1–4) $ \times$ 10$ ^{56}$ erg. A clump of CO gas was discovered 3.5 kpc above the galactic plane; it coincides with a dark lane previously found in X-ray observations, and a peak in H I emission. A comparison with H I, hot molecular hydrogen and dust suggests that the molecular gas shows signatures of warm and cool components in the outflow and tidal streams, respectively.