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Local Group Satellite Galaxies in Cosmological Simulations


Satellite dwarf galaxies are singularly useful for studies of galaxy formation because they are highly susceptible to environmental and stellar feedback effects, we can observe them in unparalleled detail in the Local Group (LG), and we can model them at high resolution in simulations. Of particular interest in galaxy formation are the Milky Way's (MW) satellites, which appear to be nearly uniformly quenched inside the MW's virial radius, likely because of both internal stellar feedback and environmental effects of the gaseous host halo. Many observational campaigns have been devoted to measuring LG satellite star formation histories and high precision proper motions from resolved stellar populations, critical to determining orbital effects on formation. However, LG surveys will revolutionize galaxy formation, only if we can provide sufficiently rigorous theoretical models to interpret them.

The spatial distribution, kinematics, and star formation histories of satellite dwarf galaxies in the LG present a unique opportunity to test galaxy formation and numerical resolution in cosmological hydrodynamic simulations. We find excellent agreement between LG observations and the inner radial distributions of ‘classical’ dwarf satellites around MW/M31-mass host galaxies from the FIRE simulations. These results also suggest potentially undiscovered classical dwarf-mass satellites in the outer halos of the MW and M31. Furthermore, we investigate the prevalence, longevity, and potential causes of so-called ‘satellite planes’ in the LG. Although satellites in the simulations are typically distributed almost isotropically around their hosts, we find that hosts with an LMC-like satellite are more likely to have MW-like satellite planes, and that M31's satellite distribution is much more common. Preliminary results on the gas content and star formation histories of simulated satellites indicate agreement with the high quenched fraction of satellites in the LG. However, the simulations and LG observations appear to be in tension with the small fraction of quenched satellites around MW analogs in the nearby universe. Our results suggest that environmental effects of the host halo may be the dominant mechanisms for quenching satellite dwarf galaxies.

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