Skip to main content

Research Repository

Advanced Search

Alignments between galaxies, satellite systems and haloes

Shao, S.; Cautun, M.; Frenk, C.S.; Gao, L.; Crain, R.A.; Schaller, M.; Schaye, J.; Theuns, T.

Alignments between galaxies, satellite systems and haloes Thumbnail


S. Shao

M. Cautun

L. Gao

R.A. Crain

M. Schaller

J. Schaye


The spatial distribution of the satellite populations of the Milky Way and Andromeda are puzzling in that they are nearly perpendicular to the discs of their central galaxies. To understand the origin of such configurations we study the alignment of the central galaxy, satellite system and dark matter halo in the largest of the ‘Evolution and Assembly of GaLaxies and their Environments’ (EAGLE) simulation. We find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of 33° in both cases. While the centrals are better aligned with the inner 10 kpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo. The central–satellite alignment is weak (median misalignment angle of 52°) and we find that around 20 per cent of systems have a misalignment angle larger than 78°, which is the value for the Milky Way. The central–satellite alignment is a consequence of the tendency of both components to align with the dark matter halo. As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo. In contrast, if the central is perpendicular to the satellite system, as in the case of the Milky Way and Andromeda, then the central–halo alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a stronger alignment with both their halo and their satellites than rotation-dominated (disc) centrals. We also found that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three.


Shao, S., Cautun, M., Frenk, C., Gao, L., Crain, R., Schaller, M., …Theuns, T. (2016). Alignments between galaxies, satellite systems and haloes. Monthly Notices of the Royal Astronomical Society, 460(4), 3772-3782.

Journal Article Type Article
Acceptance Date May 19, 2016
Online Publication Date May 24, 2016
Publication Date Aug 21, 2016
Deposit Date Sep 28, 2016
Publicly Available Date Oct 6, 2016
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 460
Issue 4
Pages 3772-3782


Published Journal Article (1.5 Mb)

Copyright Statement
This article has been published in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

You might also like

Downloadable Citations