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ABSTRACT 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 $$0.5{{\ \rm per\ cent}}$$ of the halo virial radius. These haloes contain galaxies with masses that range from ultrafaint dwarfs ($$M_\star \simeq 10^{4.5}\, \mathrm{M}_{\odot }$$) to the largest spirals ($$M_\star \simeq 10^{11}\, \mathrm{M}_{\odot }$$) 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 $$M_{\star } \sim 10^9 \, \mathrm{M}_{\odot }$$, with cores that are roughly the size of the galaxy half-light radius, rc ≃ 1−5 kpc. Furthermore, we find no evidence for core formation at radii $$\gtrsim 100\ \rm pc$$ in galaxies with M⋆/Mhalo < 5 × 10−4 or $$M_\star \lesssim 10^6 \, \mathrm{M}_{\odot }$$. 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.
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How low does it go? Too few Galactic satellites with standard reionization quenching
ABSTRACT A standard prediction of galaxy formation theory is that the ionizing background suppresses galaxy formation in haloes with peak circular velocities smaller than $$V_{\rm peak}\simeq 20 \, \rm km \, s^{-1}$$, rendering the majority of haloes below this scale completely dark. We use a suite of cosmological zoom simulations of Milky Way-like haloes that include central Milky Way disc galaxy potentials to investigate the relationship between subhaloes and ultrafaint galaxies. We find that there are far too few subhaloes within 50 kpc of the Milky Way that had $$V_{\rm peak}\gtrsim 20\, \rm km \, s^{-1}$$ to account for the number of ultrafaint galaxies already known within that volume today. In order to match the observed count, we must populate subhaloes down to $$V_{\rm peak}\simeq 6\, \rm km \, s^{-1}$$ with ultrafaint dwarfs. The required haloes have peak virial temperatures as low as 1500 K, well below the atomic hydrogen cooling limit of 104 K. Allowing for the possibility that the Large Magellanic Cloud contributes several of the satellites within 50 kpc could potentially raise this threshold to $$10\, \rm km \, s^{-1}$$ (4000 K), still below the atomic cooling limit and far below the nominal reionization threshold.
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- Award ID(s):
- 1752913
- PAR ID:
- 10174837
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 488
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 4585 to 4595
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stz1992
