CO and neutral gas in the disk of the spiral galaxy IC 342

We present "on-the-fly," fully sampled maps of CO(1-0) in the central 15' o f the spiral galaxy IC 342. In addition to the bright CO nuclear peak, ther e is a prominent CO 2'x5' bar and an extensive CO disk. The bar and nucleus contain 30% of the total observed CO emission in IC 342. Beyond the bar th e CO disk contains two spiral arms, which coincide with the two inner optic al arms. The substantial inter-arm CO component within this inner region ha s a mean surface density of 8 M-. pc(-2), close to the mean surface density of 10 M-. pc(-2), that extends to a radius of 7' (4 kpc). The total inferr ed H-2 mass is 7 x 10(8) M-. which is 30% of the total H I mass. We combine the CO data with VLA H I maps to obtain a map of the total gas surface den sity (Sigma (HI) + Sigma (H2)) in IC 342. The gas surface density shows a c entrally peaked disk, dominated by H-2 to a radius of 5' (3 kpc). Spiral ar ms run continuously from the inner to outer galaxy, transitioning smoothly from predominantly molecular in the inner galaxy to predominantly atomic at large radii. On a global scale, the gas surface density is spatially corre lated with optical spiral arm structure. On 1' (600 pc) scales the disk dis plays bar and arm asymmetries, azimuthal displacements of CO and H I emissi on, and structure that becomes increasingly complex with increasing galacti c radii. We find an excellent correlation between 21 cm radio continuum and the total gas surface density.