Atomic and molecular gas in the starburst galaxy NGC 4945 ? , ? ?

Spatial and kinematical correlations between the H i and 12CO(2−1) emission of the southern spiral galaxy NGC4945 are studied with a common angular resolution of ∼ 23′′ (corresponding to 750 pc at D = 6.7 Mpc) and a velocity resolution of ∼7 kms−1. The 1.4 GHz continuum emission is also observed. The H i kinematics yield a galaxy mass of ∼ 1.4× 10 M within radius R=380′′, with molecular and neutral atomic gas each contributing ∼2%, respectively. A central continuum source of size 7 . ′′6× 3 . ′′4 (250× 110 pc) is enveloped by a molecular cloud of mass 1.5× 10 M for R ≤ 7 . ′′5, and is rapidly rotating with Vrot ∼ 160 kms−1. H i emission from the central region at velocities |V−Vsys| > 200 km s−1 may be related to optically detected gas that is believed to trace an outflow directed towards the halo. Nuclear H i absorption at V – Vsys ∼ +80kms−1 suggests inflow towards the centre, that was so far only seen in molecular lines. H i features at each end of the major axis (|R| ∼ 600′′) are interpreted as spiral arms that are viewed tangentially and that also cause prominent emission features in the radio continuum, H i, and CO further inside the galaxy. A central elongated region showing non-circular motions is interpreted as a bar which fuels the nuclear starburst. The H i and CO position-velocity data have been analysed using linear resonance theory, and possible locations of resonances are identified.