EDGE: Globular Cluster-like Dwarf Galaxies in Cold and Warm Dark Matter

The fundamental nature of dark matter is critical to understanding the formation of dark matter halos and the galaxies they host. Due to being extremely dark matter dominated, the smallest galaxies in the universe, dwarf galaxies, provide an ideal astrophysical environment with which to study the nature of dark matter on galactic scales. While cold dark matter (CDM) has been the leading model of structure formation, tensions with observations at galactic scales suggest exploring dark matter candidates beyond the CDM paradigm. Warm dark matter (WDM) candidates predict a lack of structures on dwarf scales. We utilize the high resolution Engineering Dwarfs at Galaxy’s Edge (EDGE) hydrodynamical simulation suite to study the cosmological formation of the smallest dwarf galaxies that form in them, globular cluster-like dwarf galaxies (GCDs)—a new class of objects that share traits of both dwarf galaxies and globular clusters. Like dwarf galaxies, these objects form in dark matter halos, but with very low masses (halo masses between ~10⁶ and 10⁷ Msun), and thus have small age dispersions similar to globular clusters. We analyze GCDs in the EDGE2 suite, which includes updated physics such as radiative transfer and non-equilibrium cooling, and find that in CDM, they have far lower stellar masses of ~10² Msun. This is due to the fact that including radiative feedback prevents additional stars from forming. We present their observable properties, including their V-band magnitudes, metallicity ratios and dispersions, and age spreads. None form in WDM with 3 and 6 keV thermal relic masses. The confirmation of even a single GCD candidate would place strong constraints on WDM. Upcoming surveys such as Rubin and Roman will have the sensitivity to detect such candidates.