Earth-mass haloes and the emergence of NFW density profiles

Angulo, Raul E.; Hahn, Oliver; Ludlow, Aaron D.; Bonoli, Silvia

Abstract

We simulate neutralino dark matter (χDM) haloes from their initial collapse, at ∼ earth mass, up to a few percent solar. Our results confirm that the density profiles of the first haloes are described by a ∼r−1.5 power law. As haloes grow in mass, their density profiles evolve significantly. In the central regions, they become shallower and reach on average ∼r−1, the asymptotic form of an NFW profile. Using non-cosmological controlled simulations, we observe that temporal variations in the gravitational potential caused by major mergers lead to a shallowing of the inner profile. This transformation is more significant for shallower initial profiles and for a higher number of merging systems. Depending on the merger details, the resulting profiles can be shallower or steeper than NFW in their inner regions. Interestingly, mergers have a much weaker effect when the profile is given by a broken power law with an inner slope of −1 (such as NFW or Hernquist profiles). This offers an explanation for the emergence of NFW-like profiles: after their initial collapse, r−1.5 χDM haloes suffer copious major mergers, which progressively shallows the profile. Once an NFW-like profile is established, subsequent merging does not change the profile anymore. This suggests that halo profiles are not universal but rather a combination of (1) the physics of the formation of the microhaloes and (2) their early merger history – both set by the properties of the dark matter particle – as well as (3) the resilience of NFW-like profiles to perturbations.

Citation

Angulo, R. E., Hahn, O., Ludlow, A. D., & Bonoli, S. (2017). Earth-mass haloes and the emergence of NFW density profiles. Monthly Notices of the Royal Astronomical Society, 471(4), 4687-4701. https://doi.org/10.1093/mnras/stx1658

• Journal Article Type: Article
• Acceptance Date: Jun 29, 2017
• Online Publication Date: Jul 7, 2017
• Publication Date: Nov 11, 2017
• Deposit Date: Oct 12, 2017
• Publicly Available Date: Oct 12, 2017
• 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: 471
• Issue: 4
• Pages: 4687-4701
• DOI: https://doi.org/10.1093/mnras/stx1658