Be it therefore resolved: cosmological simulations of dwarf galaxies with extreme resolution

Coral Wheeler (Caltech)
Friday, January 18, 2019 - 12:15pm

The currently favored cosmological paradigm — Lambda Cold Dark Matter Theory (LCDM) — has been widely successful in predicting the counts, clustering, colors, morphologies, and evolution of galaxies on large scales, as well as a variety of cosmological observables. Despite these successes, several challenges have arisen to this model in recent years, most of them occurring at the smallest scales — those of dwarf galaxies (Mstar < 10^9 Msun). To investigate these challenges, I will introduce a suite of extremely high-resolution cosmological (GIZMO/FIRE2) simulations of dwarf galaxies (Mhalo ~10^10 Msun), run to z = 0 with 30 Msun resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with Mhalo & 10^8.6 Msun is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. This new generation of simulations allows us to probe smaller physical scales than previously possible in cosmological simulations, and to make more detailed predictions for the star formation histories, morphologies and kinematics of the lowest mass galaxies ever observed. We confirm many results at lower resolution, suggesting that our simulations are numerically robust (for a given physical model), but we also discover an intriguing discrepancy at the extremely low mass end of the mass-metallicity relation. Finally, we predict the existence of a large population of extremely low-surface brightness dwarfs that may go undetected for some time, and investigate the difference between observed and simulated ultra-faint dwarfs in the mass-size plane

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