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Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM?

Borukhovetskaya, Alexandra; Navarro, Julio F; Errani, Raphaël; Fattahi, Azadeh

Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM? Thumbnail


Authors

Alexandra Borukhovetskaya

Julio F Navarro

Raphaël Errani



Abstract

The unusually low velocity dispersion and large size of Crater II pose a challenge to our understanding of dwarf galaxies in the Lambda cold dark matter (LCDM) cosmogony. The low velocity dispersion suggests either a dark halo mass much lower than the minimum expected from hydrogen cooling limit arguments or one that is in the late stages of extreme tidal stripping. The tidal interpretation has been favoured in recent work and is supported by the small pericentric distances consistent with available kinematic estimates. We use N-body simulations to examine this interpretation in detail, assuming a Navarro–Frenk–White (NFW) profile for Crater II’s progenitor halo. Our main finding is that, although the low velocity dispersion can indeed result from the effect of tides, the large size of Crater II is inconsistent with this hypothesis. This is because galaxies stripped to match the observed velocity dispersion are also reduced to sizes much smaller than the observed half-light radius of Crater II. Unless its size has been substantially overestimated, reconciling this system with LCDM requires that either (i) it is not bound and near equilibrium (unlikely, given its crossing time is shorter than the time elapsed since pericentre) or (ii) its progenitor halo deviates from the assumed NFW profile. The latter alternative may signal that baryons can affect the inner halo cusp even in extremely faint dwarfs or, more intriguingly, may signal effects associated with the intimate nature of the dark matter, such as finite self-interactions, or other such deviations from the canonical LCDM paradigm.

Citation

Borukhovetskaya, A., Navarro, J. F., Errani, R., & Fattahi, A. (2022). Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM?. Monthly Notices of the Royal Astronomical Society, 512(4), 5247-5257. https://doi.org/10.1093/mnras/stac653

Journal Article Type Article
Acceptance Date Mar 2, 2022
Online Publication Date Mar 11, 2022
Publication Date 2022-06
Deposit Date Jun 28, 2022
Publicly Available Date Mar 28, 2024
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 512
Issue 4
Pages 5247-5257
DOI https://doi.org/10.1093/mnras/stac653

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Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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