Be it therefore resolved: Cosmological Simulations of Dwarf Galaxies with Extreme Resolution

Coral Wheeler; Philip F. Hopkins; Andrew B. Pace; Shea Garrison-Kimmel; Michael Boylan-Kolchin; Andrew Wetzel; James S. Bullock; Dusan Keres; Claude-Andre Faucher-Giguere; Eliot Quataert

doi:10.1093/mnras/stz2887

paper

Be it therefore resolved: Cosmological Simulations of Dwarf Galaxies with Extreme Resolution

arXiv:1812.02749 · doi:10.1093/mnras/stz2887

Abstract

We study a suite of extremely high-resolution cosmological FIRE simulations of dwarf galaxies ( $M_{halo} ≲ 1 0^{10}$ $M_{⊙}$ ), run to $z = 0$ with $30 M_{⊙}$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{halo} ≳ 1 0^{8.6} M_{⊙}$ is populated by a resolved {\em stellar} galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{*} < 1 0^{5} M_{⊙}$ ) have their star formation truncated early ( $z ≳ 2$ ), likely by reionization, while classical dwarfs ( $M_{*} > 1 0^{5} M_{⊙}$ ) continue forming stars to $z < 0.5$ . The systems have bursty star formation (SF) histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with $M_{*} / M_{halo} > 1 0^{- 4}$ to form a dark matter core $> 200$ pc, while lower-mass UFDs exhibit cusps down to $≲ 100$ pc, as expected from energetic arguments. Our dwarfs with $M_{*} > 1 0^{4} M_{⊙}$ have half-mass radii ( $R_{1/2}$ ) in agreement with Local Group (LG) dwarfs; dynamical mass vs. $R_{1/2}$ and the degree of rotational support also resemble observations. The lowest-mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (e.g. LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that our simulations are numerically robust (for a given physical model).

arXiv comment14 pages; 9 figures; 1 table; submitted to MNRAS

Be it therefore resolved: Cosmological Simulations of Dwarf Galaxies with Extreme Resolution

Abstract

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