The Local Group on FIRE: dwarf galaxy populations across a suite of hydrodynamic simulations

We present a new set of high-resolution hydrodynamic cosmological zoom-in simulations that apply the Feedback In Realistic Environments physics to both Local Group (LG)-like and isolated MilkyWay (MW)-like volumes (10 host systems in total with a baryonic particle mass similar or equal to 3500-7000 M-circle dot). We study the stellar mass functions, circular velocity or mass profiles, and velocity dispersions of the dwarf galaxy populations. The simulations reproduce the stellar mass function and central densities of MW satellite dwarfs for M-* >= 10(5.5) M-circle dot and predict the existence of similar to 3 unidentified galaxies with M-* similar to 10(5) M-circle dot within 300 kpc of the MW. Overall, we find no evidence for the classical missing satellites or too-big-to-fail (TBTF) problems for satellite galaxies in our sample. Among the satellites, TBTF is resolved primarily by subhalo disruption and overall mass-loss; central density profiles of subhaloes are of secondary importance. For non-satellite galaxies, our LG-like simulations predict as many as similar to 10 as-of-yet unseen galaxies at distances 0.3-1 Mpc from both hosts, with M-* similar or equal to 10(5-6) M-circle dot (in haloes with V-max similar to 20 km s(-1)), albeit with large halo-to-halo variance. None of our simulations produces a compact, baryon-dominated, high-density dwarf elliptical-type galaxy (with V-circ greater than or similar to 35 km s(-1) at r < 1 kpc), of which six may appear in the LG (but none in the MW). It may therefore remain a challenge to reproduce the full diversity of the dwarf population, including both the highest and lowest density systems.