RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 04 April 2019, 11:00-12:00; CSO Common Room

Melanie Chevance

"The Physics Driving the Molecular Cloud Lifecycle during Galaxy Formation and Evolution"

The cloud-scale physics of star formation and feedback represent the main uncertainties in galaxy formation and evolution studies. In recent years, it has become clear that the “star formation relation” between the gas mass (surface density) and the star formation rate (surface density) depends strongly on the spatial scale. We have shown that this multi-scale nature of the star formation relation is a direct probe of the cloud-scale physics of star formation and feedback. By quantifying the details of this scale dependence, we can directly measure fundamental quantities describing star formation and feedback, such as molecular cloud lifetimes, star formation efficiencies, feedback timescales, feedback outflow velocities, feedback coupling efficiencies, and coherence length scales. While these quantities were previously only accessible in the Local Group, it is now possible to measure them across a representative part of the galaxy population, from the nearby Universe out to high redshift (z > 2). I will present the first systematic characterisation of the evolutionary timeline of molecular clouds and star-forming regions using the above method, across a wide variety of galactic environments. I will show that star formation is regulated by efficient stellar feedback, driving GMC dispersal on short timescales (1-5 Myr) due to radiation and stellar winds, prior to supernova explosions. This feedback limits GMC lifetimes to about one dynamical timescale (10-30 Myr), with integrated star formation efficiencies of only a few percent. Our findings reveal that galaxies consist of building blocks undergoing vigorous, feedback-driven lifecycles, that vary with the galactic environment and collectively define how galaxies form stars. These observations settle a long-standing question on the multi-scale lifecycle of gas and stars in galaxies, and open up the exciting prospect of characterising cloud-scale star formation and feedback during galaxy formation and evolution.