Dark matter is the most abundant form of matter in the universe, yet its properties remain the most obscure. It is only observable through its gravitational effects on baryonic matter, most notably through its shaping of galaxies. Two main models exist: Cold Dark Matter (CDM), whose particles interact only through gravity, and Self-Interacting Dark Matter (SIDM), where DM particles also interact with each other through a non-zero cross section. For this study, I used three Milky Way–like cosmological simulations from the Feedback in Realistic Environments-2 (FIRE-2) suite. Each simulation has a CDM, SIDM1, and SIDM10 version, allowing for a direct comparison of the models — where SIDM1 and SIDM10 represent interactions with cross sections of 1 and 10 cm2/g, respectively, meaning SIDM10 has 10 times stronger dark matter interactions.

The analysis focuses on the low-mass end of the stellar mass–halo mass (SMHM) relation, where the scatter is largest, as the high-mass end is already well characterized in the literature. The results show that the choice of dark matter model has little effect on this scatter. However, the stellar half-mass radius plots highlight differences in how the models influence the internal distribution of stars within galaxies. Preliminary results indicate that galaxies formed in the CDM model may develop flatter stellar density profiles compared to those formed in SIDM.