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The SIBELIUS Project: E Pluribus Unum

Sawala, Till; McAlpine, Stuart; Jasche, Jens; Lavaux, Guilhem; Jenkins, Adrian; Johansson, Peter H; Frenk, Carlos S

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Till Sawala

Stuart McAlpine

Jens Jasche

Guilhem Lavaux

Peter H Johansson


We introduce ‘Simulations Beyond The Local Universe’ (SIBELIUS) that connect the Local Group (LG) to its cosmic environment. We show that introducing hierarchical small-scale perturbations to a density field constrained on large scales by observations provides an efficient way to explore the sample space of LG analogues. From more than 60 000 simulations, we identify a hierarchy of LG characteristics emanating from different scales: the total mass, orientation, orbital energy, and the angular momentum are largely determined by modes above λ = 1.6 comoving Mpc (cMpc) in the primordial density field. Smaller scale variations are mostly manifest as perturbations to the MW–M31 orbit, and we find that the observables commonly used to describe the LG – the MW–M31 separation and radial velocity – are transient and depend on specifying scales down to 0.2 cMpc in the primordial density field. We further find that the presence of M33/LMC analogues significantly affects the MW–M31 orbit and its sensitivity to small-scale perturbations. We construct initial conditions that lead to the formation of an LG whose primary observables precisely match the current observations.


Sawala, T., McAlpine, S., Jasche, J., Lavaux, G., Jenkins, A., Johansson, P. H., & Frenk, C. S. (2022). The SIBELIUS Project: E Pluribus Unum. Monthly Notices of the Royal Astronomical Society, 509(1), 1432-1446.

Journal Article Type Article
Acceptance Date Sep 7, 2021
Online Publication Date Nov 12, 2021
Publication Date 2022-01
Deposit Date Feb 7, 2022
Publicly Available Date Feb 8, 2022
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 509
Issue 1
Pages 1432-1446


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Copyright Statement
© The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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