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ABSTRACT A variety of observational campaigns seek to test dark matter models by measuring dark matter subhaloes at low masses. Despite their predicted lack of stars, these subhaloes may be detectable through gravitational lensing or via their gravitational perturbations on stellar streams. To set measurable expectations for subhalo populations within Lambda cold dark matter, we examine 11 Milky Way (MW)-mass haloes from the FIRE-2 baryonic simulations, quantifying the counts and orbital fluxes for subhaloes with properties relevant to stellar stream interactions: masses down to $$10^{6}\, \text{M}_\odot$$, distances ≲50 kpc of the galactic centre, across z = 0 − 1 (tlookback = 0–8 Gyr). We provide fits to our results and their dependence on subhalo mass, distance, and lookback time, for use in (semi)analytical models. A typical MW-mass halo contains ≈16 subhaloes $$\gt 10^{7}\, \text{M}_\odot$$ (≈1 subhalo $$\gt 10^{8}\, \text{M}_\odot$$) within 50 kpc at z ≈ 0. We compare our results with dark matter-only versions of the same simulations: because they lack a central galaxy potential, they overpredict subhalo counts by 2–10×, more so at smaller distances. Subhalo counts around a given MW-mass galaxy declined over time, being ≈10× higher at z = 1 than at z ≈ 0. Subhaloes have nearly isotropic orbital velocity distributions at z ≈ 0. Across our simulations, we also identified 4 analogues of Large Magellanic Cloud satellite passages; these analogues enhance subhalo counts by 1.4–2.1 times, significantly increasing the expected subhalo population around the MW today. Our results imply an interaction rate of ∼5 per Gyr for a stream like GD-1, sufficient to make subhalo–stream interactions a promising method of measuring dark subhaloes.
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Galactic potential constraints from clustering in action space of combined stellar stream data
ABSTRACT Stream stars removed by tides from their progenitor satellite galaxy or globular cluster act as a group of test particles on neighbouring orbits, probing the gravitational field of the Milky Way. While constraints from individual streams have been shown to be susceptible to biases, combining several streams from orbits with various distances reduces these biases. We fit a common gravitational potential to multiple stellar streams simultaneously by maximizing the clustering of the stream stars in action space. We apply this technique to members of the GD-1, Palomar 5 (Pal 5), Orphan, and Helmi streams, exploiting both the individual and combined data sets. We describe the Galactic potential with a Stäckel model, and vary up to five parameters simultaneously. We find that we can only constrain the enclosed mass, and that the strongest constraints come from the GD-1, Pal 5, and Orphan streams whose combined data set yields $$M(\lt 20\, \mathrm{kpc}) = 2.96^{+0.25}_{-0.26} \times 10^{11} \, \mathrm{ M}_{\odot}$$. When including the Helmi stream in the data set, the mass uncertainty increases to $$M(\lt 20\, \mathrm{kpc}) = 3.12^{+3.21}_{-0.46} \times 10^{11} \, \mathrm{M}_{\odot}$$.
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- Award ID(s):
- 2007232
- PAR ID:
- 10283668
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 502
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 4170 to 4193
- 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/stab304
