Forged in FIRE: Cusps, cores and baryons in low-mass dwarf galaxies

Jose Oñorbe*, Michael Boylan-Kolchin, James S. Bullock, Philip F. Hopkins, Dušan Kereš, Claude André Faucher-Giguère, Eliot Quataert, Norman Murray

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

306 Scopus citations

Abstract

We present multiple ultrahigh resolution cosmological hydrodynamic simulations of M* ≃ 104-6.3 M dwarf galaxies that form within two Mvir = 109.5-10 M dark matter halo initial conditions. Our simulations rely on the Feedback in Realistic Environments (FIRE) implementation of star formation feedback and were run with high enough force and mass resolution to directly resolve structure on the ~200 pc scales. The resultant galaxies sit on the M* versus Mvir relation required to match the Local Group stellar mass function via abundance matching. They have bursty star formation histories and also form with half-light radii and metallicities that broadly match those observed for local dwarfs at the same stellar mass. We demonstrate that it is possible to create a large (~1 kpc) constant-density dark matter core in a cosmological simulation of an M* ≃ 106.3 M dwarf galaxy within a typical Mvir = 1010 M halo - precisely the scale of interest for resolving the 'too big to fail' problem. However, these large cores are not ubiquitous and appear to correlate closely with the star formation histories of the dwarfs: dark matter cores are largest in systems that form their stars late (z ≲ 2), after the early epoch of cusp building mergers has ended. Our M* ≃ 104 M dwarf retains a cuspy dark matter halo density profile that matches that of a dark-matter-only run of the same system. Though ancient, most of the stars in our ultrafaint form after reionization; the ultraviolet field acts mainly to suppress fresh gas accretion, not to boil away gas that is already present in the protodwarf.

Original languageEnglish (US)
Pages (from-to)2092-2106
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume454
Issue number2
DOIs
StatePublished - Dec 1 2015

Funding

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. JO and JSB were supported by NSF grant AST-1009999 and NASA grant NNX09AG01G. JO thanks the financial support of the Fulbright/MICINN Program. JO also thanks the PYNBODY team for making this software publicly available. DK was supported by a Hellman Fellowship and NSF grant AST-1412153. C-AF-G was supported by NSF through grant AST-1412836, by NASA through grant NNX15AB22G, and by Northwestern University funds.

Keywords

  • Cosmology: theory
  • Galaxies: dwarf
  • Galaxies: evolution
  • Galaxies: formation
  • Methods: numerical

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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