Scatter, bias, and chaos of satellite orbits in triaxial dark matter haloes
- 1Department of Astronomy, Yale University , New Haven, CT 06511 ,
Abstract
The pericentric distances of satellite galaxies govern their tidal stripping, quenching, and survival, yet their orbits are almost universally computed in spherical host haloes, whereas dark matter haloes are generically triaxial. We quantify, orbit by orbit, the error this simplification incurs. We integrate 106 satellites, drawn from a cosmological infall distribution, in static Navarro–Frenk–White (NFW) hosts of systematically varying triaxiality at fixed mass profile. Triaxiality leaves the population medians of pericentre, apocentre, and orbital period essentially unchanged. Instead, successive pericentres of an individual orbit scatter by 5–23 per cent depending on host shape, irrespective of orbital energy; the minimum pericentre distance reached within a Hubble time shrinks systematically by up to 21 per cent, enhancing the peak tidal mass loss. This triaxiality-driven orbital dephasing is overwhelmingly regular rather than chaotic; chaotic satellite orbits are common and dominate the near-centre pericentric passages in strongly flattened hosts, but diverge on time-scales far exceeding the Hubble time. Satellite orbits spherically reconstructed via direct backward integration in a truly triaxial host diverge by a tenth of the virial radius within 2–4 Gyr, with comparable uncertainties sourced separately by the unconstrained shape of the host and by its unknown absolute orientation. For the Milky Way dwarf Triangulum II, the unknown halo shape and orientation alone spread the inferred pericentre by ∼ 50 per cent, five times its reported uncertainty and more than ten times the Large Magellanic Cloud-induced shift, and bias it by 6–70 per cent. This host-shape uncertainty can dominate satellite orbital error budgets and should be incorporated in future inferences.
Versions
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BibTeX
@article{chiang2026scatter,
title = {{Scatter, bias, and chaos of satellite orbits in triaxial dark matter haloes}},
author = {Barry T Chiang and Frank C van den Bosch and Michael A Keim},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1919},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1919/8885808},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Scatter, bias, and chaos of satellite orbits in triaxial dark matter haloes
AU - Barry T Chiang
AU - Frank C van den Bosch
AU - Michael A Keim
PY - 2026
DA - 2026/10/08
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1919
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1919/8885808
AB - The pericentric distances of satellite galaxies govern their tidal stripping, quenching, and survival, yet their orbits are almost universally computed in spherical host haloes, whereas dark matter haloes are generically triaxial. We quantify, orbit by orbit, the error this simplification incurs. We integrate 10^6 satellites, drawn from a cosmological infall distribution, in static Navarro–Frenk–White (NFW) hosts of systematically varying triaxiality at fixed mass profile. Triaxiality leaves the population medians of pericentre, apocentre, and orbital period essentially unchanged. Instead, successive pericentres of an individual orbit scatter by 5–23 per cent depending on host shape, irrespective of orbital energy; the minimum pericentre distance reached within a Hubble time shrinks systematically by up to 21 per cent, enhancing the peak tidal mass loss. This triaxiality-driven orbital dephasing is overwhelmingly regular rather than chaotic; chaotic satellite orbits are common and dominate the near-centre pericentric passages in strongly flattened hosts, but diverge on time-scales far exceeding the Hubble time. Satellite orbits spherically reconstructed via direct backward integration in a truly triaxial host diverge by a tenth of the virial radius within 2–4 Gyr, with comparable uncertainties sourced separately by the unconstrained shape of the host and by its unknown absolute orientation. For the Milky Way dwarf Triangulum II, the unknown halo shape and orientation alone spread the inferred pericentre by ∼ 50 per cent, five times its reported uncertainty and more than ten times the Large Magellanic Cloud-induced shift, and bias it by 6–70 per cent. This host-shape uncertainty can dominate satellite orbital error budgets and should be incorporated in future inferences.
SN - 0035-8711
SN - 1365-2966
ER -