Journal Article

The shape of dark matter haloes in the Aquarius simulations: evolution and memory

Carlos A. Vera-Ciro, Laura V. Sales, Amina Helmi, Carlos S. Frenk, Julio F. Navarro, Volker Springel, Mark Vogelsberger and Simon D. M. White

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1377-1391
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19134.x
The shape of dark matter haloes in the Aquarius simulations: evolution and memory

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We use the high-resolution cosmological N-body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time, evolving from a typically prolate configuration at early stages to a more triaxial/oblate geometry at the present day. This evolution in halo shape correlates well with the distribution of the infalling material: prolate configurations arise when haloes are fed through narrow filaments, which characterizes the early epochs of halo assembly, whereas triaxial/oblate configurations result as the accretion turns more isotropic at later times. Interestingly, at redshift z= 0, clear imprints of the past history of each halo are recorded in their shapes at different radii, which also exhibit a variation from prolate in the inner regions to triaxial/oblate in the outskirts. Provided that the Aquarius haloes are fair representatives of Milky Way like 1012 M objects, we conclude that the shape of such dark matter haloes is a complex, time-dependent property, with each radial shell retaining memory of the conditions at the time of collapse.

Keywords: galaxies: evolution; galaxies: formation; galaxies: haloes; dark matter

Journal Article.  10506 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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