The structure and evolution of the interstellar medium (ISM) strongly dictate galactic gas dynamics, star formation (SF), and galaxy evolution. While recent studies emphasize the rapid formation and destruction of molecular structures by stellar feedback (Schinnerer & Leroy 2024), this conflicts with the observed deficiency of HI gas expected from such destruction. Here, I revisit the alternative paradigm: that molecular structures survive long-term and evolve primarily via galactic dynamics. Using ALMA observations of M83 and 12 nearby galaxies from the FACTS survey, I show that molecular cloud properties evolve alongside large-scale galactic structures. This is supported by correlations between environment, CO 2–1/1–0 line ratios, and cloud boundedness. Crucially, stellar feedback enhances CO ratios only near HII regions and fails to increase velocity dispersions, implying limited feedback-driven turbulence. Instead of undergoing rapid destruction, molecular clouds persist, coagulating and fragmenting via galactic dynamical processes. This framework shifts SF theory from the collapse of diffuse gas toward identifying triggers within long-lived clouds, redefining galactic dynamics as a system governed by the motion of discrete molecular structures rather than pure hydrodynamics.
Contact local & organisation : Suzanne MADDEN
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