ALMA obs. toward NGC 5253. I. Molecular clouds

We have identified 118 molecular clouds with average values of 4.3 pc in radius and 2.2km/s in velocity dispersion, which comprise the molecular cloud complexes observed previously with ~100pc resolution. We derive for the first time in this galaxy the I(CO)-N(H_2_) conversion factor, X=4.1_-2.4_^+5.9^x10^20^cm^-2^(K.km/s)^-1^, based on the virial method.

The line width and mass-to-size relations of the resolved molecular clouds present an offset on average toward higher line widths and masses with respect to quiescent regions in other nearby spiral galaxies and our Galaxy. The offset in the scaling relation reaches its maximum in regions close to the central starburst, where velocity dispersions are ~0.5dex higher and gas mass surface densities are as high as {Sigma}_H2_=10^3^M_{sun}/pc^2^.