Atomic and Molecular Gas in the Starburst Galaxy NGC4945

Spatial and kinematical correlations between HI and CO (2-1) emission of the southern spiral galaxy NGC4945 are studied with a common angular (23 arcsec) and velocity resolution (7 km/s). The 21cm continuum emission is also observed. The HI kinematics yield a galaxy mass of 1.4x10^{11} Mo within a radius of 380 arcsec, with molecular and neutral atomic gas each contributing 2%. Nuclear HI absorption at velocities 80 km/s higher than systemic indicates gas flowing towards the centre. HI features at each end of the major axis (R ~ 600 arcsec) are interpreted as spiral arms that are viewed tangentially and that also cause prominent emission features in the radio continuum, HI, and CO further inside the galaxy. A central elongated region showing non-circular motions is interpreted as a bar which fuels the nuclear starburst. HI and CO position-velocity data have been analysed using linear resonance theory and possible locations of resonances are identified.Comment: 16 pages, Latex file, 9 Postscript Figures, aa.cls and psfig.sty included. Accepted by Astronomy and Astrophysic