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The tangential velocity excess of the Milky Way satellites

Cautun, Marius; Frenk, Carlos S.

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Authors

Marius Cautun



Abstract

We estimate the systemic orbital kinematics of the Milky Way classical satellites and compare them with predictions from the Λ cold dark matter (ΛCDM) model derived from a semi-analytical galaxy formation model applied to high-resolution cosmological N-body simulations. We find that the Galactic satellite system is atypical of ΛCDM systems. The subset of 10 Galactic satellites with proper motion measurements has a velocity anisotropy, β = −2.2 ± 0.4, which lies in the 2.9 per cent tail of the ΛCDM distribution. Individually, the Milky Way satellites have radial velocities that are lower than expected for their proper motions, with 9 out of the 10 having at most 20 per cent of their orbital kinetic energy invested in radial motion. Such extreme values are expected in only 1.5 per cent of ΛCDM satellites systems. In the standard cosmological model, this tangential motion excess is unrelated to the existence of a Galactic ‘disc of satellites’. We present theoretical predictions for larger satellite samples that may become available as more proper motion measurements are obtained.

Citation

Cautun, M., & Frenk, C. S. (2017). The tangential velocity excess of the Milky Way satellites. Monthly Notices of the Royal Astronomical Society: Letters, 468(1), L41-L45. https://doi.org/10.1093/mnrasl/slx025

Journal Article Type Article
Acceptance Date Feb 6, 2017
Online Publication Date Feb 8, 2017
Publication Date Jun 11, 2017
Deposit Date Jun 19, 2017
Publicly Available Date Mar 29, 2024
Journal Monthly Notices of the Royal Astronomical Society: Letters
Electronic ISSN 1745-3933
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 468
Issue 1
Pages L41-L45
DOI https://doi.org/10.1093/mnrasl/slx025

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





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