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

Creators: Wheeler, Coral; Oñorbe, José; Bullock, James S.; Boylan-Kolchin, Michael; Elbert, Oliver; Garrison-Kimmel, Shea; Hopkins, Philip F.; Kereš, Dušan

Abstract

We present Feedback in Realistic Environment (FIRE)/GIZMO hydrodynamic zoom-in simulations of isolated dark matter haloes, two each at the mass of classical dwarf galaxies (M_(vir) ≃ 10^(10) M_⊙) and ultra-faint 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 subhaloes, many of which form stars. Each of our dwarfs with M_★ ≃ 10^6 M_⊙ has 1–2 well-resolved satellites with M_★ = 3-200 × 10^3 M_⊙. Even our isolated ultra-faint galaxies have star-forming subhaloes. If this is representative, dwarf galaxies throughout the Universe should commonly host tiny satellite galaxies of their own. We combine our results with the Exploring the Local Volume in Simulations (ELVIS) simulations to show that targeting ∼ 50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ∼35 per cent compared to random 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_⊙ haloes. 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 haloes hosting reionization 'fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization.

Additional Information

© 2015. The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 July 23. Received 2015 July 22; in original form 2015 May 6. First published online August 24, 2015. We thank M. C. Cooper for helpful discussions. This work used computational resources granted by NASA Advanced Supercomputing (NAS) Division, NASA Center for Climate Simulation, Teragrid and by the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number OCI-1053575 and ACI-1053575, the latter through allocation AST140080 (PI: Boylan-Kolchin). Support for this work was also provided by NASA through Hubble Space Telescope theory grants (programs AR-12836 and AR-13888) from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. CW and OE were supported by Hubble Space Telescope grants HST-AR-13921.002-A and HST-AR-13888.003-A, and SGK by the National Science Foundation Grant AST-1009999. Support for PFH was provided by the Gordon and Betty Moore Foundation through Grant 776 to the Caltech Moore Center for Theoretical Cosmology and Physics, an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant 1411920. DK received support from National Science Foundation grant number AST-1412153, funds from the University of California, San Diego and XSEDE allocation TG-AST-120025.

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Published - MNRAS-2015-Wheeler-1305-16.pdf

Submitted - 1504.02466v1.pdf

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