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Combining observations of multiple CO lines with radiative transfer modelingis a very powerful tool to investigate the physical properties of the moleculargas in galaxies. Using new observations as well as literature data, we providethe most complete CO ladders ever generated for eight star-forming regions inthe spiral arms and inter-arms of the spiral galaxy NGC 6946, with observationsof the CO(1-0), CO(2-1), CO(3-2), CO(4-3), CO(6-5), 13CO(1-0) and 13CO(2-1)transitions. For each region, we use the large velocity gradient assumption toderive beam-averaged molecular gas physical properties, namely the gas kinetictemperature (T_K), H2 number volume density n(H2) and CO number column densityN(CO). Two complementary approaches are used to compare the observations withthe model predictions: chi-square minimisation and likelihood. The physicalconditions derived vary greatly from one region to the next: T_K=10-250 K,n(H2)=10^2.3-10^7.0 cm^-3 and N(CO)=10^15.0-10^19.3 cm^-2. The spectral lineenergy distribution (SLED) of some of these extranuclear regions indicates astar-formation activity that is more intense than that at the centre of our ownMilky Way. The molecular gas in regions with a large SLED turnover transition(J_max>4) is hot but tenuous with a high CO column density, while that inregions with a low SLED turnover transition (J_max<=4) is cold but dense with alow CO column density. We finally discuss and find some correlations betweenthe physical properties of the molecular gas in each region and the presence ofyoung stellar population indicators (supernova remnants, HII regions, HI holes,etc.)

Molecular Gas Properties of the Giant Molecular Cloud Complexes in the Arms and Inter-arms of the Spiral Galaxy NGC 6946