Skip to main content

Research Repository

Advanced Search

The velocity anisotropy of the Milky Way satellite system

Riley, Alexander H; Fattahi, Azadeh; Pace, Andrew B; Strigari, Louis E; Frenk, Carlos S; Gómez, Facundo A; Grand, Robert JJ; Marinacci, Federico; Navarro, Julio F; Pakmor, Rüdiger; Simpson, Christine M; White, Simon DM

The velocity anisotropy of the Milky Way satellite system Thumbnail


Alexander H Riley

Andrew B Pace

Louis E Strigari

Facundo A Gómez

Robert JJ Grand

Federico Marinacci

Julio F Navarro

Rüdiger Pakmor

Christine M Simpson

Simon DM White


We analyse the orbital kinematics of the Milky Way (MW) satellite system utilizing the latest systemic proper motions for 38 satellites based on data from Gaia Data Release 2. Combining these data with distance and line-of-sight velocity measurements from the literature, we use a likelihood method to model the velocity anisotropy, β, as a function of Galactocentric distance and compare the MW satellite system with those of simulated MW-mass haloes from the APOSTLE and Auriga simulation suites. The anisotropy profile for the MW satellite system increases from β ∼ −2 at r ∼ 20 kpc to β ∼ 0.5 at r ∼ 200 kpc, indicating that satellites closer to the Galactic centre have tangentially-biased motions while those farther out have radially-biased motions. The motions of satellites around APOSTLE host galaxies are nearly isotropic at all radii, while the β(r) profiles for satellite systems in the Auriga suite, whose host galaxies are substantially more massive in baryons than those in APOSTLE, are more consistent with that of the MW satellite system. This shape of the β(r) profile may be attributed to the central stellar disc preferentially destroying satellites on radial orbits, or intrinsic processes from the formation of the Milky Way system.


Riley, A. H., Fattahi, A., Pace, A. B., Strigari, L. E., Frenk, C. S., Gómez, F. A., …White, S. D. (2019). The velocity anisotropy of the Milky Way satellite system. Monthly Notices of the Royal Astronomical Society, 486(2), 2679-2694.

Journal Article Type Article
Acceptance Date Apr 4, 2019
Online Publication Date Apr 5, 2019
Publication Date Jun 30, 2019
Deposit Date Apr 9, 2019
Publicly Available Date Apr 9, 2019
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 486
Issue 2
Pages 2679-2694


Accepted Journal Article (1.5 Mb)

Copyright Statement
© 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.

You might also like

Downloadable Citations