Warm gas and spatial variations of molecular excitation in the nuclear region of IC 342

Maps of the J = 1-0 and J = 2-1 lines of CO-12, CO-13 and CO-18 in the nuclear region of the galaxy IC 342 are presented. Observational data obtained with the IRAM 30-m telescope give new information on the spatial variation of excitation, density, and column density of molecular and atomic material in the nuclear region of IC 342. A first qualitative inspection of the data indicates that the molecular gas temperature in the central few hundred pc of IC 342 is significantly higher than in the disk region in IC 342 and the Galaxy. A more detailed model of the CO excitation and radiative transfer is then discussed. New far-infrared measurements of the fine-structured 63-micron forbidden line of O I indicate that the atomic and molecular gas pressures are both a few times 100,000/cu cm K and 10 times larger than in the Galaxy.