Implications of a contracted dark matter halo for the Milky Way’s inferred virial mass

Dado, D, Brown, ST, Fattahi, A, Font, AS ORCID: 0000-0001-8405-9883 and McCarthy, IG ORCID: 0000-0002-1286-483X (2026) Implications of a contracted dark matter halo for the Milky Way’s inferred virial mass. Monthly Notices of the Royal Astronomical Society, 552 (4). ISSN 0035-8711

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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 (Formula presented) 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 (Formula presented) on average ((Formula presented) for some systems), and the concentration by a factor of (Formula presented). 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 (Formula presented) largely eliminate the mean bias for all models. The local dark matter density at the Solar radius is recovered to within (Formula presented) % 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 (Formula presented). We additionally find a halo-to-halo scatter of (Formula presented) dex ((Formula presented) %) persists even under idealized conditions, setting a likely lower limit for the precision of halo mass estimates.

Item Type:	Article
Uncontrolled Keywords:	galaxies: evolution; galaxies: kinematics and dynamics; dark matter; astro-ph.GA; astro-ph.GA; 5101 Astronomical Sciences; 51 Physical Sciences; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	23 September 2026
Date of first compliant Open Access:	4 November 2026
Date Deposited:	04 Nov 2026 14:47
Last Modified:	04 Nov 2026 14:47
DOI or ID number:	10.1093/mnras/stag1865
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29820

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