2003A&A...404..495I

We present J=2-1, J=3-2, J=4-3 ¹²CO and 492GHz [CI] maps as well as J=2-1 and J=3-2 ¹³CO measurements of the central regions in the nearby Sc galaxies IC 342 and Maffei 2. In both galaxies, the distribution of CO and [CI] is strongly concentrated towards the center. These centers harbour modest starbursts. Both galaxies have nearly identical ¹²CO transitional ratios but the relative intensities of their ¹³CO and [CI] emission lines differ significantly. The observed sets of line intensities require modelling with a multi-component molecular gas. In both galaxies, a dense component must be present (n(H₂)≃10⁴-10⁵cm^–3) with kinetic temperatures T_kin=10-20K (IC 342) or 20-60K (Maffei 2), as well as a less dense (IC 342: a few hundred cm^–3 at most; Maffei 2: ≃3x10³cm^–3) and hotter (T_kin=100-150K) component. In both galaxies, neutral and ionized atomic carbon amounts are between 1.5 and 2.5 times those of CO. In both starburst centers about half to two thirds of the molecular gas mass is associated with the hot PDR phase. The center of IC 342 contains within R=0.25kpc an (atomic and molecular) gas mass of 1x10⁷M_☉ and a peak face-on gas mass density of about 70M_☉/pc². For Maffei 2 these numbers are less clearly defined, mainly because of uncertainties in its distance and carbon abundance. We find a gass mass M_gas≥0.5x10⁷M_☉, and a peak face-on gas mass density of about 35M_☉/pc².