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What to expect from dynamical modelling of galactic haloes

Wang, Wenting; Han, Jiaxin; Cole, Shaun; Frenk, Carlos; Sawala, Till

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Wenting Wang

Jiaxin Han

Till Sawala


Many dynamical models of the Milky Way halo require assumptions that the distribution function of a tracer population should be independent of time (i.e. a steady-state distribution function) and that the underlying potential is spherical. We study the limitations of such modelling by applying a general dynamical model with minimal assumptions to a large sample of galactic haloes from cosmological N-body and hydrodynamical simulations. Using dark matter particles as dynamical tracers, we find that the systematic uncertainties in the measured mass and concentration parameters typically have an amplitude of 25–40 per cent. When stars are used as tracers, however, the systematic uncertainties can be as large as a factor of 2–3. The systematic uncertainties are not reduced by increasing the tracer sample size and vary stochastically from halo to halo. These systematic uncertainties are mostly driven by underestimated statistical noise caused by correlated phase-space structures that violate the steady-state assumption. The number of independent phase-space structures inferred from the uncertainty level sets a limiting sample size beyond which a further increase no longer significantly improves the accuracy of dynamical inferences. The systematic uncertainty level is determined by the halo merger history, the shape and environment of the halo. Our conclusions apply generally to any spherical steady-state model.


Wang, W., Han, J., Cole, S., Frenk, C., & Sawala, T. (2017). What to expect from dynamical modelling of galactic haloes. Monthly Notices of the Royal Astronomical Society, 470(2), 2351-2366.

Journal Article Type Article
Acceptance Date May 26, 2017
Online Publication Date Jun 1, 2017
Publication Date Sep 11, 2017
Deposit Date Aug 4, 2017
Publicly Available Date Aug 4, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 470
Issue 2
Pages 2351-2366


Published Journal Article (1.9 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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