Thursday, November 14, 2019, 11:00am to 12:00pm
The physics driving the molecular cloud lifecycle during galaxy formation and evolution
Abstract: The cloud-scale physics of star formation and feedback represent the main uncertainties in galaxy formation and evolution simulations. I will present our group's efforts towards overcoming this problem by using empirical constraints on the molecular cloud lifecycle to motivate the next generation of sub-grid models in galaxy simulations. Specifically, I will show that the multi-scale nature of the star formation relation between the gas mass and the star formation rate is a direct probe of the cloud-scale physics of star formation and feedback. As such, it represents a fundamental test for star formation and feedback models applied in numerical simulations of nearby and distant galaxies. Using this scale dependence, we can now 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 our group’s first results showing that molecular clouds in nearby star-forming galaxies undergo universally fast and inefficient star formation, due to short molecular cloud lifetimes (10-30 Myr) and rapid cloud destruction by stellar feedback (1-5 Myr), causing them to reach integrated star formation efficiencies of only 2-10%. These findings reveal that galaxies consist of building blocks undergoing vigorous, feedback-driven life cycles that vary with the galactic environment and collectively define how galaxies form stars. Throughout this talk, I will present examples of applying these empirical insights in detailed numerical simulations of galaxy formation and evolution, showing that the large-scale properties of the galaxy population are shaped by cloud-scale baryonic physics.