Ultralight dark matter halos have central solitons and the soliton mass is correlated with the overall halo mass. However, the exact form of the “core-halo” relation that sets the ratio of these masses is not well understood. However, realistic halos will form via asymmetric collapse and we show that simulations with aspherical initial conditions lead to more complicated solitons than their spherical counterparts.
Abstract
Ultralight dark matter (ULDM) is an interesting alternative to the cold dark matter (CDM) paradigm. Due to the extremely low mass of the constituent particle (∼10−22eV), ULDM can exhibit quantum effects up to kiloparsec scales. In particular, runaway collapse in the centres of ULDM halos is prevented by quantum pressure, providing a possible resolution to the ‘core-cusp problem’ of CDM. However, the the detailed relationship between the ULDM core mass and that of the overall halo is poorly understood. We simulate the collapse of both spherical and aspherical isolated ULDM overdensities using AxioNyx, finding that the central cores of collapsed halos undergo sustained oscillatory behaviour which affects both their peak density and overall morphology. The variability in core morphology increases with the asphericity of the initial overdensity and remnants of initial asphericity persist long after collapse. Furthermore, the peak central densities are higher in spherical configurations. Consequently, astrophysically realistic halos may exhibit substantial departures from theoretical core-halo profiles and we would expect a significant variance of the properties of halos with the same mass.
- Kendall, Gosenca and Easther
- Aspherical ULDM Collapse: Variation in the Core-Halo Mass Relation
- Monthly Notices of the Royal Astronomical Society, 526 (1) or ArXiV:2305.10340
Density distributions across each plane (y–z, x–z, and x–y) a triaxial collapse simulation, observed at a redshift of 0.3