Abstract. The galaxy NGC 253 is a well-known nearby spiral galaxy showing numerous peculiar features (e.g. a nuclear ring, gas outflow, a bar, and a warp) which we study using tracers of the different gas phases. Its large starburst activity places NGC 253 among the most prominent extragalactic sources from the radio range over the entire IR range to X-rays. Whereas the X-rays trace the hottest gas component, the Halpha emission, e.g., shows the distribution of the ionized gas at several thousand Kelvin. The warm component of the neutral gas is best studied through the HI line emission, and CO is usually used as a tracer of the cold molecular gas phase. In this short contribution I concentrate on the neutral gas component of NGC 253 which we studied in HI with the Australia Telescope Compact Array (ATCA) and in CO (J=1-0) with the Swedish-ESO Submillimeter Telescope (SEST) at La Silla (Chile). In addition I will briefly summarize other molecular lines observed in NGC 253, which is in fact the richest extragalactic molecular source both in terms of line strength and number of molecular species detected.
First results of the HI observations have been published by Koribalski, Whiteoak, & Houghton (1995) . Whereas the HI emission traces the large-scale distribution and kinematics of the neutral atomic gas, the HI absorption against the central continuum emission allows a glimpse into the dynamics of the cool gas (T approx. 100 K) in the nuclear region.
Keywords. galaxies: individual (NGC 253) - galaxies: starburst.