Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

Abstract

We present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark matter halos, two each at the mass of classical dwarf galaxies (M vir 10 10 M ) and ultrafaint galaxies (M vir 10 9 M ), and with two feedback implementations. The resulting central galaxies lie on an extrapolated abundance matching relation from M 10 6 to 10 4 M without a break. Every host is filled with subhalos, many of which form stars. Our dwarfs with M 10 6 M each have 1 − 2 well-resolved satellites with M = 3 − 200 × 10 3 M . Even our isolated ultra-faint galaxies have star-forming subhalos. If this is representative, dwarf galaxies throughout the universe should commonly host tiny satellite galaxies of their own. We combine our results with the ELVIS simulations to show that targeting ∼ 50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ∼ 35% compared to random halo pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target.The well-resolved ultra-faint galaxies in our simulations (M 3 − 30 × 10 3 M ) form within M peak 0.5 − 3 × 10 9 M halos. Each has a uniformly ancient stellar population (> 10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that M halo 5 × 10 9 M is a probable dividing line between halos hosting reionization "fossils" and those hosting dwarfs that can continue to form stars in isolation after reionization.

Constraints on the star formation efficiency of galaxies during the epoch of reionization

“…Accurate determination of the SMHM relation also relies on appropriate treatments of different feedback mechanisms, as demonstrated by recent simulations of dwarf galaxies (e.g. Wheeler et al 2015) which suggest a lower SMHM ratio than Behroozi et al (2013b) and Behroozi & Silk (2015). Nonetheless, given the qualitative similarity between the two independent methods and the large uncertainties associated with both of them, we do not pursue the explanation further.…”

Farthest Neighbor: The Distant Milky Way Satellite Eridanus II*

“…As a quiescent dwarf galaxy located close to, but beyond, the virial radius of Milky Way, EriII is a key object for studying environmental influences on low-mass galaxies and the quenching of star formation in such systems (Weisz et al 2014;Wetzel et al 2015;Wheeler et al 2015;Fillingham et al 2016).…”

High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

“…Other recent work that contains identical FIRE code and methods include Oñorbe et al (2015), Chan et al (2015), Ma et al (2015), Faucher-Giguère et al (2015), and Wheeler et al (2015).…”