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Evolution of galactic planes of satellites in the eagle simulation

Shao, Shi; Cautun, Marius; Frenk, Carlos S

Evolution of galactic planes of satellites in the eagle simulation Thumbnail


Marius Cautun


We study the formation of planes of dwarf galaxies around Milky Way (MW)-mass haloes in the EAGLE galaxy formation simulation. We focus on satellite systems similar to the one in the MW: spatially thin or with a large fraction of members orbiting in the same plane. To characterize the latter, we introduce a robust method to identify the subsets of satellites that have the most coplanar orbits. Out of the 11 MW classical dwarf satellites, 8 have highly clustered orbital planes whose poles are contained within a 22° opening angle centred around (l, b) = (182°, −2°). This configuration stands out when compared to both isotropic and typical ΛCDM satellite distributions. Purely flattened satellite systems are short-lived chance associations and persist for less than 1Gyr⁠. In contrast, satellite subsets that share roughly the same orbital plane are longer lived, with half of the MW-like systems being at least 4Gyr old. On average, satellite systems were flatter in the past, with a minimum in their minor-to-major axes ratio about 9Gyr ago, which is the typical infall time of the classical satellites. MW-like satellite distributions have on average always been flatter than the overall population of satellites in MW-mass haloes and, in particular, they correspond to systems with a high degree of anisotropic accretion of satellites. We also show that torques induced by the aspherical mass distribution of the host halo channel some satellite orbits into the host’s equatorial plane, enhancing the fraction of satellites with coplanar orbits. In fact, the orbital poles of coplanar satellites are tightly aligned with the minor axis of the host halo.


Shao, S., Cautun, M., & Frenk, C. S. (2019). Evolution of galactic planes of satellites in the eagle simulation. Monthly Notices of the Royal Astronomical Society, 488(1), 1166-1179.

Journal Article Type Article
Acceptance Date Jun 20, 2019
Online Publication Date Jun 26, 2019
Publication Date Sep 30, 2019
Deposit Date Oct 8, 2019
Publicly Available Date Oct 8, 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 488
Issue 1
Pages 1166-1179


Published Journal Article (897 Kb)

Copyright Statement
This article has been accepted for publication in the Monthly notices of the Royal Astronomical Society ©: 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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