The clouds of M82. I: HCN in the South-West part

High sensitivity, high angular and spectral resolution interferometric observations of the HCN(1-0) line in the South-West inner part of the starburst galaxy M 82 are presented. The feature interpreted by Nakai et al. (1987) as a molecular ring is resolved into a clumpy substructure where the clumps have sizes and masses comparable to Galactic Giant Molecular Cloud complexes. The combination of our data with other observations strongly suggests a picture of the interstellar medium in M 82 as a huge photodissociation/photoionization region with embedded tiny, hot, dense molecular cores. Although the absence of supernova remnants towards the molecular peaks seems to contradict massive star formation, we argue that star formation does take place inside the molecular clumps