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The lifecycle of molecular clouds in nearby galaxies

Presentation #223.03 in the session “Assessing the Impact of Stellar Feedback”.

Published onJan 11, 2021
The lifecycle of molecular clouds in nearby galaxies

The cycling of matter in galaxies between molecular clouds, stars and feedback is a major driver of galaxy evolution. However, it remains a major challenge to derive a theory of how galaxies turn their gas into stars and how stellar feedback affects the subsequent star formation on the cloud scale, as a function of the galactic environment. Star formation in galaxies is expected to be highly dependent on the galactic structure and dynamics, because it results from a competition between mechanisms such as gravitational collapse, shear, spiral arm passages, cloud-cloud collisions, and feedback processes such as supernovae, stellar winds, photoionization and radiation pressure. A statistically representative sample of galaxies is therefore needed to probe the wide range of conditions under which stars form. I will present the first systematic characterisation of the evolutionary timeline of the giant molecular cloud (GMC) lifecycle, star-formation and feedback in the PHANGS sample of star-forming disc galaxies. I will show that GMC are short-lived (10-30 Myr) and are dispersed after about one dynamical timescale by stellar feedback, between 1 and 5 Myr after massive stars emerge. Although the coupling efficiency of early feedback mechanisms such as radiation and stellar winds is limited to a few tens of percent, it is sufficient to disperse the parent molecular cloud prior to supernova explosions. This limits the integrated star formation efficiencies of GMCs to 2 to 10 per cent. These findings reveal that star formation in galaxies is fast and inefficient, and is governed by cloud-scale, environmentally-dependent, dynamical processes. These measurements constitute a fundamental test for numerical sub-grid recipes of star-formation and feedback in simulations of galaxy formation and evolution.

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