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Baryon-driven decontraction in Milky Way-mass haloes

Forouhar Moreno, Victor J and Benítez-Llambay, Alejandro and Cole, Shaun and Frenk, Carlos (2022) 'Baryon-driven decontraction in Milky Way-mass haloes.', Monthly Notices of the Royal Astronomical Society, 511 (3). pp. 3910-3921.


We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simulation to study their inner dark matter (DM) content and how baryons alter it. As in previous studies, we find that all haloes are more massive at the centre compared to their dark matter-only (DMO) counterparts at the present day as a result of the dissipational collapse of baryons during the assembly of the galaxy. However, we identify two processes that can reduce the central halo mass during the evolution of the galaxy. First, gas blowouts induced by active galactic nuclei feedback can lead to a substantial decrease of the central DM mass. Secondly, the formation of a stellar bar and its interaction with the DM can induce a secular expansion of the halo; the rate at which DM is evacuated from the central region by this process is related to the average bar strength, and the time-scale on which it acts determines how much the halo has decontracted. Although the inner regions of the haloes we have investigated are still more massive than their DMO counterparts at z = 0, they are significantly less massive than in the past and less massive than expected from the classic adiabatic contraction model. Since the MW has both a central supermassive black hole and a bar, the extent to which its halo has contracted is uncertain. This may affect estimates of the mass of the MW halo and of the expected signals in direct and indirect DM detection experiments.

Item Type:Article
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Publisher statement:© 2022 The Author(s) 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.
Date accepted:01 February 2022
Date deposited:21 June 2022
Date of first online publication:03 February 2022
Date first made open access:21 June 2022

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