The nucleus of the nearby galaxy IC 342

To study the different components of the molecular gas in the nuclear regio n of the nearby spiral galaxy IC342, (CO)-C-12 (3-2), 13CO (3-2) and (2-1), as well as HCN (1-0) through (4-3) observations are presented and analyzed in conjunction with a variety of line and continuum emission data of the l iterature. We find several giant molecular clouds embedded in a medium with lower column and volume density. The gas shows strong density and temperat ure gradients with a very clumpy substructure; the lower-density gas is rat her warm (less than or equal to 50 K) and the temperature decreases with in creasing density. While LVG calculations are contradicting our observations , we are able to explain all CO and [C II] line data by applying a model of photon dominated regions (PDR); for the gas seen in these lines we find no evidence for an additional dominant heating mechanism. On the other hand, for our HCN observations tracing the dense gas clumps (n(H-2) approximate t o 10(6) cm(-3)) where the influence of UV photons is expected to be less im portant than for less dense gas seen in CO (n(H-2) approximate to 10(4) cm( -3)), an LVG model approach should be applicable and, in fact, yields resul ts which fit well the data and support the outlined scenario. For this gas component which is rather cool (T-k less than or equal to 30 K), heating pr ocesses involving photoelectrons should be unimportant and other mechanisms like turbulent energy dissipation or cosmic rays should be considered. The structure of the nucleus of IC342 with several giant molecular clouds with sizes of less than or equal to 20 to 50 pc and masses of order 10(6) M-cir cle dot partly associated with H II regions and embedded into a lower-densi ty interstellar medium shows striking similarities in terms of cloud distri bution and their physical behaviour with our Galactic Centre region.