Over 85% of all matter in the Universe is comprised of dark matter, yet we are unable to measure or view it by any conventional methods save for its gravitational signature. Given how much of the Universe we strive to understand is composed of this mysterious substance, it's imperative that we attempt to understand it as well to complete our theories of how everything came to be. We currently have two major theories of this mysterious matter: CDM (Cold Dark Matter) and SIDM (Self-Interacting Dark Matter). However we have no way to conduct experiments with these theories, as we cannot constrain this matter. Enter the suite of FIRE-2 simulations: large scale simulations of galactic formation obeying baryonic physics and employing the characteristics of varying DM models, such as CDM and SIDM. 

In this poster, we present an updated and novel algorithm for tracking stellar subhalos and substructure through time in these simulations, and produce datasets of their final resting places and properties. We include whether they remain dwarfs, evolve into streams, or diffuse into phase-mixed objects, and keep record of their infall times, masses, positions, and velocities. We report this with the hopes that it may be used to constrain the properties of SIDM, as we compare substructure statistics in both models. Our tracking pipeline is accurate to a high degree on average, and successfully recovers the majority of all stars after merging events throughout the course of galactic formation. 

We find that there is no statistical difference between the CDM and SIDM models across a myriad of parameters. The proportions of dwarfs formed vs streams formed vs phase-mixed objects formed are largely similar in simulations’ respective CDM and SIDM versions. Furthermore we find that the distributions of their masses, infall times, and distances from the main halo (within the virial radius) are all statistically the same (p > 0.5). 

In the future, we hope to map corresponding present-day substructure between CDM and SIDM by analyzing the initial conditions in both simulations, and then conduct a case-by-case analysis of each object to look for deeper comparisons. We also hope to continue our analysis into the chemodynamics of recovered substructure as well, to investigate whether SIDM can be constrained from a chemical/metallicity perspective. Lastly, we plan to apply the tracking pipeline to all Milky Way-mass galaxies in the FIRE-2 suite of simulations and generate a comprehensive new catalog with all substructure properties and notes for future use in any projects