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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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This content will become publicly available on September 16, 2026
Semianalytic Modeling of Dark Matter Subhalo Encounters with Thin Stellar Streams: Statistical Predictions for GD-1-like Streams in Cold Dark Matter
Abstract Stellar streams from disrupted globular clusters are dynamically cold structures that are sensitive to perturbations from dark matter subhalos, allowing them in principle to trace the dark matter substructure in the Milky Way. We model, within the context of Λ cold dark matter, the likelihood of dark matter subhalos to produce a significant feature in a GD-1-like stream and analyze the properties of such subhalos. We generate many realizations of the subhalo population within a Milky Way mass host halo using the semianalytic codeSatGen, accounting for effects such as tidal stripping and dynamical friction. The subhalo distributions are combined with a GD-1-like stream model, and the impact of subhalos that pass close to the stream are modeled withGala. We find that subhalos with masses in the range 2 × 106M⊙–108M⊙at the time of the stream–subhalo encounter, corresponding to masses of about 2 × 107M⊙–109M⊙at the time of infall, are the likeliest to produce gaps in a GD-1-like stream. We find that gaps occur on average ∼3 times per realization of the host system. These gaps have typical widths of ∼(5–27)° and fractional underdensities of ∼(10–30)%, with larger gaps being caused by heavier subhalos. The stream–subhalo encounters responsible for these have impact parameters (0.1–1.5) kpc and relative velocities ∼(200–410) km s−1. We also investigate the effects of increasing the host-halo mass on the gap properties and formation rate.
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- Award ID(s):
- 2210533
- PAR ID:
- 10646498
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 991
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 66
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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