A dark matter profile to model diverse feedback-induced core sizes of ACDM haloes

Alexandres Lazar*, James S. Bullock, Michael Boylan-Kolchin, T. K. Chan, Philip F. Hopkins, Andrew S. Graus, Andrew Wetzel, Kareem El-Badry, Coral Wheeler, Maria C. Straight, Dusan Keres, Claude André Faucher-Giguère, Alex Fitts, Shea Garrison-Kimmel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


We analyse the cold dark matter density profiles of 54 galaxy haloes simulated with Feedback In Realistic Environments (FIRE)-2 galaxy formation physics, each resolved within 0.5 per cent of the halo virial radius. These haloes contain galaxies with masses that range from ultrafaint dwarfs (M* ~ 104.5M) to the largest spirals (M* ˜ 1011M) and have density profiles that are both cored and cuspy. We characterize our results using a new, analytic density profile that extends the standard two-parameter Einasto form to allow for a pronounced constant density core in the resolved innermost radius. With one additional core-radius parameter, rc, this three-parameter core-Einasto profile is able to characterize our feedback-impacted dark matter haloes more accurately than other three-parameter profiles proposed in the literature. To enable comparisons with observations, we provide fitting functions for rc and other profile parameters as a function of both M* and M/Mhalo. In agreement with past studies, we find that dark matter core formation is most efficient at the characteristic stellar-to-halo mass ratio M/Mhalo ˜5 × 10-3, or M* ˜ 109 M, with cores that are roughly the size of the galaxy half-light radius, rc ˜ 15kpc. Furthermore, we find no evidence for core formation at radii > 100 pc in galaxies with M*/Mhalo < 5 × 10-4 or M*-106M. For Milky Way-size galaxies, baryonic contraction often makes haloes significantly more concentrated and dense at the stellar half-light radius than DMO runs. However, even at the Milky Way scale, FIRE-2 galaxy formation still produces small dark matter cores of ˜ 0.5-2 kpc in size. Recent evidence for a ~2 kpc core in the Milky Way's dark matter halo is consistent with this expectation.

Original languageEnglish (US)
Pages (from-to)2393-2417
Number of pages25
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Sep 1 2020


  • Dark matter
  • Galaxies: evolution
  • Galaxies: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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