Spatially Resolved Star Formation in Cosmological Zoom-in Simulations: Understanding the Role of Feedback in Scaling Relations

Citation

Orr, Matthew Edward (2019) Spatially Resolved Star Formation in Cosmological Zoom-in Simulations: Understanding the Role of Feedback in Scaling Relations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WE1D-5586. https://resolver.caltech.edu/CaltechTHESIS:05142019-152545186

Abstract

To understand the night sky is to understand how galaxies form their stars. Cosmological zoom-in simulations, which self-consistently evolve a small number of galaxies at very high resolution by embedding them within a fully cosmological box, have evolved over the last 25 years to a level of realism where they can begin to tackle questions of spatially resolved star formation within galaxies. Whereas a decade ago simulations faced difficulty in matching even global properties of observed galaxies (e.g., the ratio of stellar mass to total halo mass), the state of the art is now able to meaningfully recover resolved quantities in galaxies that were not put into the simulations by hand (e.g., the Kennicutt-Schmidt star formation scaling relation).

The research presented in this thesis seeks to understand how the physics of star formation and stellar feedback from massive stars shape and regulate the interstellar medium (ISM) within galaxies. Particularly, the focus lies on the scale of the largest coherent structures in galaxies -- the disk scale height. To explore these physics, the cosmological zoom-in simulations of the Feedback in Realistic Environments (FIRE) project (Hopkins et al. 2014, 2018) are used.

The chapters of this thesis explore various topics in spatially resolved star formation, including: the Kennicutt-Schmidt relation (Schmidt 1959, Kennicutt 1998), an empirical relation between gas surface density and star formation rates, in the FIRE-1 simulations (Orr et al. 2018), including an examination what set the extent of the star-forming disks in the simulations (i.e., what causes star formation to fire up in the outskirts); an examination of the observational method of analyzing stacks of galaxy observations, finding that temporal variations in spatially resolved star formation rates within individual galaxies were more than enough to bias stacking analysis of star formation rate profiles; a semi-analytic model of non-equilibrium star formation rates, relating to the competition between the feedback timescale associated with star formation and local dynamical times (Orr et al. 2019), which explores this as a source of scatter in the Kennicutt-Schmidt relation; and finally, investigating how gas velocity dispersions and star formation rates relate in FIRE-2 Milky Way-mass disk galaxies, exploring whether or not feedback is primarily driving the velocity dispersions in galaxies, and how quickly local patches can self-regulate with star formation (Orr et al. in prep.).

Thesis Files