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Molecular gas is the fuel for star formation in galaxies. Using observations from the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) survey, that spatially resolve (1-30 pc) individual molecular clouds across the Hubble sequence, we reveal a clear dependence of the nature of the molecular interstellar medium of galaxies on Hubble type, and present a simple diagnostic of cloud formation. In particular, we highlight the shortcomings of the usual virial approach to clouds as self-gravitating objects, and stress the importance of the external galactic potential and in-plane shear to regulate the dynamical states of clouds. We also introduce a simple but powerful cloud-cloud collision formalism that accounts for the cloud properties in both nearby and high-redshift systems. Finally, we discuss the impact of these different mechanisms on the star formation efficiency of the clouds and thus the quenching of star formation, particularly in galaxy nuclei and spheroids (morphological quenching). |
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