Implications of a contracted dark matter halo for the Milky Way’s inferred virial mass
4 affiliations
- 1Institute for Computational Cosmology, Department of Physics, Durham University , South Road, Durham DH1 3LE ,
- 2Centre for Extragalactic Astronomy, Department of Physics, Durham University , South Road, Durham DH1 3LE ,
- 3The Oskar Klein Centre, Department of Physics, Stockholm University , Albanova University Center, SE-106 91 Stockholm ,
- 4Astrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,
Abstract
We investigate how reliably the global properties of Milky Way-mass dark matter haloes can be recovered from dynamical data from a limited range of radii, particularly ≲ 30 kpc where observations are most sensitive but baryonic processes modify the halo structure. Using the ARTEMIS (Assembly of high-ResoluTion Eagle simulations of MIlkyWay-type galaxieS) simulations, which produce varying degrees of baryon-induced contraction, we fit dark matter profiles over restricted radial ranges using commonly adopted parametric models. Assuming negligible observational uncertainties allows the systematic errors from these choices to be isolated. When fits are confined to inner radii, a Navarro–Frenk–White (NFW) profile underestimates the virial mass by a factor of ≈ 2 on average (≈ 4 for some systems), and the concentration by a factor of ≈ 2. Einasto and generalized-NFW models provide excellent local fits but retain similar global biases. In contrast, a contracted halo prescription yields stable extrapolations and recovers unbiased halo mass estimates over all radii. The inferred mass improves systematically with increasing radial coverage, and tracers beyond ≳ 50 kpc largely eliminate the mean bias for all models. The local dark matter density at the Solar radius is recovered to within ≲ 5% for all profiles other than NFW. These biases are sufficient to reconcile recent low Milky Way-mass estimates derived from inner rotation-curve analyses with the canonical ≈ 1012 M⊙. We additionally find a halo-to-halo scatter of ≳ 0.1 dex (≈ 25%) persists even under idealized conditions, setting a likely lower limit for the precision of halo mass estimates.
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BibTeX
@article{dado2026implications,
title = {{Implications of a contracted dark matter halo for the Milky Way’s inferred virial mass}},
author = {Diego Dado and Shaun T Brown and Azadeh Fattahi and Andreea S Font and Ian G McCarthy},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1865},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1865/8859319},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Implications of a contracted dark matter halo for the Milky Way’s inferred virial mass
AU - Diego Dado
AU - Shaun T Brown
AU - Azadeh Fattahi
AU - Andreea S Font
AU - Ian G McCarthy
PY - 2026
DA - 2026/10/01
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1865
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1865/8859319
AB - We investigate how reliably the global properties of Milky Way-mass dark matter haloes can be recovered from dynamical data from a limited range of radii, particularly ≲ 30 kpc where observations are most sensitive but baryonic processes modify the halo structure. Using the ARTEMIS (Assembly of high-ResoluTion Eagle simulations of MIlkyWay-type galaxieS) simulations, which produce varying degrees of baryon-induced contraction, we fit dark matter profiles over restricted radial ranges using commonly adopted parametric models. Assuming negligible observational uncertainties allows the systematic errors from these choices to be isolated. When fits are confined to inner radii, a Navarro–Frenk–White (NFW) profile underestimates the virial mass by a factor of ≈ 2 on average (≈ 4 for some systems), and the concentration by a factor of ≈ 2. Einasto and generalized-NFW models provide excellent local fits but retain similar global biases. In contrast, a contracted halo prescription yields stable extrapolations and recovers unbiased halo mass estimates over all radii. The inferred mass improves systematically with increasing radial coverage, and tracers beyond ≳ 50 kpc largely eliminate the mean bias for all models. The local dark matter density at the Solar radius is recovered to within ≲ 5% for all profiles other than NFW. These biases are sufficient to reconcile recent low Milky Way-mass estimates derived from inner rotation-curve analyses with the canonical ≈ 10^12 M_⊙. We additionally find a halo-to-halo scatter of ≳ 0.1 dex (≈ 25%) persists even under idealized conditions, setting a likely lower limit for the precision of halo mass estimates.
SN - 0035-8711
SN - 1365-2966
ER -