Emission of CO, CI, and CII in the spiral arms of M83 and M51

We present a detailed study of photon dominated regions at several spiral arm positions and the centers of the nearby spiral galaxies M51 and M83. For this, we combine all important cooling lines: [CI] 609 mu m taken at the JCMT with (CO)-C-12 and (CO)-C-13 1-0 and 2-1 lines taken at the IRAM 30m MRT. These transitions are combined with data taken from the literature: ISO/L VS [CII] 158 mu m, [OI] 63 mu m, 146 mu m, and [NII] (122 mu m) data [1] and mid-J CO lines from [2,3,4].