Atomic and molecular gas in the starburst galaxy NGC 4945 ^*,**

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia

Corresponding author: R. Wielebinski, rwielebinski@mpifr-bonn.mpg.de

Received: 24 September 1998
Accepted: 2 April 2001

Abstract

Spatial and kinematical correlations between the Hi and ¹²CO(2-1) emission of the southern spiral galaxy NGC 4945 are studied with a common angular resolution of ~23'' (corresponding to 750 pc at Mpc) and a velocity resolution of ~7 . The 1.4 GHz continuum emission is also observed. The Hi kinematics yield a galaxy mass of ~ within radius , with molecular and neutral atomic gas each contributing ~2% , respectively. A central continuum source of size 76 34 (250 110 pc) is enveloped by a molecular cloud of mass for R ≤ 75, and is rapidly rotating with . Hi emission from the central region at velocities V_sys > 200 may be related to optically detected gas that is believed to trace an outflow directed towards the halo. Nuclear Hi absorption at V -V_sys ~ +80 suggests inflow towards the centre, that was so far only seen in molecular lines. Hi features at each end of the major axis ( ~ 600'') 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. The Hi and CO position-velocity data have been analysed using linear resonance theory, and possible locations of resonances are identified.