The Temperature Distribution of Dense Molecular Gas in Starburst Cores

摘要

We present interferometric maps of ammonia within the cores of a sample of eight prominent, southern starburst galaxies. The observations were performed with the Australia Telescope Compact Array. In six galaxies the metastable ammonia (1,1) and (2,2) inversion lines were detected in absorption or emission or both. For some galaxies we also show ammonia (3,3) maps. Ammonia is a tracer of dense molecular gas (densities > 104 cm–2) and most of that material appears to be stored at vertices of optical dust features. The ammonia (1,1) and (2,2) transitions are used to compute rotational temperatures. Those temperatures are with ~ 25 – 35 K relatively uniform for all galaxies and correspond to kinetic temperatures of ~ 40 – 60 K. The ammonia masses visible in the cores of the galaxies are ~ 1 – 35 M. The dynamics of the dense molecular gas exhibit non-circular motions in NGC 4945 and in NGC 253. The kinematics cannot be described by a simple coherent structure. We also report the first detection of ammonia in the prototypical ultra-luminous far infrared galaxy Arp 220 for which first results indicate an extremely high rotational temperature of ~ 100 K.