Axion dark matter, solitons and the cusp–core problem

By D. Marsh, A. Pop. 2015

228 citations recorded by the source corpus.

Self-gravitating bosonic fields can support stable and localised field configurations. For real fields, these solutions oscillate in time and are known as oscillatons. The density profile is static, and is soliton. Such solitons should be ubiquitous in models of axion dark matter, with the soliton characteristic mass and size depending on some inverse power of the axion mass. Stable configurations of non-relativistic axions are studied numerically using the Schr\"{o}dinger-Poisson system. This method, and the resulting soliton density profiles, are reviewed. Using a scaling symmetry and the uncertainty principle, the core size of the soliton can be related to the central density and axion mass, $m_a$, in a universal way. Solitons have a constant central density due to pressure-support, unlike the cuspy profile of cold dark matter (CDM). One consequence of this fact is that solitons composed of ultra-light axions (ULAs) may resolve the `cusp-core' problem of CDM. In DM halos, thermodynamics will lead to a CDM-like Navarro-Frenk-White profile at large radii, with a central soliton core at small radii. Using Monte-Carlo techniques to explore the possible density profiles of this form, a fit to stellar-kinematical data of dwarf spheroidal galaxies is performed. In order for ULAs to resolve the cusp-core problem (without recourse to baryon feedback or other astrophysical effects) the axion mass must satisfy $m_a<1.1\times 10^{-22}\text{ eV}$ at 95\% C.L. On the other hand, ULAs with $m_a\lesssim 1\times 10^{-22}\text{ eV}$ are in some tension with cosmological structure formation. An axion solution to the cusp-core problem thus makes novel predictions for future measurements of the epoch of reionisation. On the other hand, this can be seen as evidence that structure formation could soon impose a \emph{Catch 22} on axion/scalar field DM, similar to the case of warm DM.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9e1bce458923c3dd95c083c458aa39cc7413d5e5

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Citations in the corpus

Constraining the mass of light bosonic dark matter using SDSS Lyman-α forest (2017, methodology): “…observed kinematic properties of some dwarf galaxies, with FDM masses ranging from ∼ 0.4 × 10−22 eV up to ∼ 4 − 6 × 10−22 eV depending on the considered objects and analysis procedure (Schive et al. 2014; Marsh & Pop 2015; Calabrese & Spergel 2016; Chen et al. 2017; GonzálesMorales et al. 2016).”
“Non-cold” dark matter at small scales: a general approach (2017, background): “5 from the kinematics of dwarf galaxies [63, 64], which were recently complemented by strong lower limits from the abundance of high-z galaxies [65], m22 > 10, superseeding earlier limits from their luminosity functions (m22 > 1.”
CONTRASTING GALAXY FORMATION FROM QUANTUM WAVE DARK MATTER, ψDM, WITH ΛCDM, USING PLANCK AND HUBBLE DATA (2015, methodology): “Marsh & Pop (2015) havealso determined a similar constraint, m 1.122 ( s2 ), by fitting the mass profiles of Fornax and Sculptor dSph galaxies to the soliton mass profile using an empirical relation between the half-light radius and velocity dispersion.”
Ultralight scalars as cosmological dark matter (2016, background): “Other estimates, based on fewer galaxies or more approximate models, are roughly consistent [16, 50, 51](8).”