Adrianne Slyz

Abstract:

Abstract Dwarf galaxies serve as powerful laboratories for investigating the underlying physics of galaxy evolution including the impact of baryonic feedback processes and external environmental influences. We compare the visual and structural properties of dwarf galaxies in ultra-deep HSC-SSP imaging of the COSMOS field with those measured from realistic HSC-like synthetic observations of dwarfs generated by the Illustris TNG50 and NewHorizon simulations. Using Sérsic profile fitting and non-parametric morphological metrics (Gini, M20, asymmetry, and concentration), we evaluate the diversity of structural properties in observed and simulated galaxies. Our analysis shows that NewHorizon and TNG50 galaxies lie at opposite extremes of observed structural trends: NewHorizon produces diffuse, extended galaxies with shallow Sérsic indices, while TNG50 yields compact, concentrated systems with steep indices. Both simulations reproduce observed structural trends more closely at higher stellar masses ($M_{\star } \sim 10^{9.5}~{\rm {\rm M}_{\odot }}$) but fail to capture the full diversity of COSMOS dwarfs at lower masses. Non-parametric metrics further show that NewHorizon galaxies exhibit more uneven, clumpy light distributions while TNG50 galaxies have smoother but excessively concentrated profiles. These structural differences reflect underlying differences in their physical prescriptions and are likely driven by differing approaches to ISM gas physics, supernova feedback and star formation in addition to differences in numerical resolution. Our findings highlight the unique power of low-mass galaxies to constrain differences in simulation physics, especially star formation and feedback prescriptions. Upcoming surveys from facilities like the Vera C. Rubin Observatory and Euclid will enable more rigorous comparisons with simulations, offering deeper insights into the physical processes shaping galaxy evolution.

Abstract:

We use the cosmological hydrodynamical simulation NewHorizon to study the effects of the baryonic component on the inner mass profile of dark matter haloes of isolated galaxies (). Dark matter deficits (‘cores’) develop only in galaxies in a narrow range of stellar mass, . The lower stellar mass limit arises because a minimum amount of star formation is required to drive the baryonic outflows that redistribute dark matter and create a core. The upper limit roughly coincides with the total amount of dark matter initially contained within the innermost 2 kpc (), which roughly coincides with the stellar half-mass radius of these dwarfs. This enclosed mass is quite insensitive to the total virial mass of the system. The same upper limit applies to other simulations, like NIHAO and EAGLE-CHT10, despite their rather different galaxy formation efficiencies. This suggests that it is the galaxy total stellar mass that determines when a core is formed, and not the galaxy-to-dark halo mass ratio, as argued in earlier work. This is consistent with a back-of-the-envelope estimate for a SN-induced rate of orbital diffusion. Although NewHorizon dwarfs reproduce the observed diversity of rotation curves better than other simulations, there are significant differences in the gravitational importance of baryons in the inner regions of dwarfs compared to observations. These differences prevent us from concluding that cosmological simulations are currently fully able to account for the observed diversity of rotation curve shapes.