Cassi Lochhaas, PhD

Because cosmological simulations cannot reach high enough resolution to self-consistently model the formation of individual stars, the formation and feedback processes from stars must be implemented as "subgrid" models. There are many choices to make for the parameters of these models: How dense should simulated gas get before it starts collapsing into stars? How massive should the newly-formed "star particles", representing clusters of stars, be? How much mass, heat, metals, and kinetic energy should each star cluster return to its surroundings (feedback)? For simulators, these questions are typically answered with whatever parameters end up producing "realistic" galaxies that follow the well-defined observed scaling relations, such as the stellar mass-halo mass relation and the mass-metallicity relation.

I am currently leading the effort to investigate different subgrid models for star formation and feedback within the framework of the existing Figuring Out Gas & Galaxies In Enzo (FOGGIE) simulations. These are cosmological zoom-in simulations that resolve the circumgalactic medium (CGM) to a high degree, but still require prescriptions for star formation and feedback inside the galaxies themselves. The primary goal of this project is to determine the star formation and feedback parameters to use for the next generation of the simulations at even higher resolution, while improving on the realism of the simulated galaxies.

The other goal of this project to investigate feedback prescriptions in FOGGIE is to determine how different forms of stellar feedback drive the kinematics in the highly-resolved CGM. Gas kinematics like turbulence are responsible for driving the CGM away from equilibrium models, but it is not yet clear exactly how turbulence and other kinematics are driven. By exploring a number of different feedback parameters and measuring the CGM turbulence, I hope to develop an understanding of how the driving of CGM kinematics are linked to processes occurring within the galaxy.