In the fuzzy dark matter (FDM) model, gravitationally collapsed objects always consist of a solitonic core located within a virialised halo. Although various numerical simulations have confirmed that the collapsed structure can be described by a cored NFW-like density profile, there is still disagreement about the relation between the core mass and the halo mass. To fully understand this relation, we have assembled a large sample of cored haloes based on both idealised soliton mergers and cosmological simulations with various box sizes. We find that there exists a sizeable dispersion in the core-halo mass relation that increases with halo mass, indicating that the FDM model allows cores and haloes to coexist in diverse configurations. We provide a new empirical equation for a core-halo mass relation with uncertainties that can encompass all previously-found relations in the dispersion, and emphasise that any observational constraints on the particle mass m using a tight one-to-one core-halo mass relation should suffer from an additional uncertainty on the order of 50 per cent for halo masses ≳ 109 (8 × 10−23 eV/(mc2))3/2 M⊙. We suggest that tidal stripping may be one of the effects contributing to the scatter in the relation.
Fuzzy dark matter (FDM) is an attractive dark matter candidate motivated by small-scale problems in astrophysics and with a rich phenomenology on those scales. We scrutinize the FDM model, more specifically the mass of the FDM particle, through a dynamical analysis for the Galactic ultrafaint dwarf (UFD) galaxies. We use a sample of 18 UFDs to place the strongest constraints to date on the mass of the FDM particle, updating on previous bounds using a subset of the sample used here. We find that most of the sample UFDs prefer an FDM particle mass heavier than 10−21 eV. In particular, Segue 1 provides the strongest constraint, with m ψ = 1.1 − 0.7 + 8.3 × 10 − 19 eV . The constraints found here are the first that are compatible with various other independent cosmological and astrophysical bounds found in the literature, in particular with the latest bounds using the Lyα forest. We also find that the constraints obtained in this work are not compatible with the bounds from luminous dwarf galaxies, as already pointed out in the previous work using UFDs. This could indicate that although a viable dark matter model, it might be challenging for the FDM model to solve the small-scale problems.
We investigate the basic properties of voids from high resolution, cosmological N-body simulations of Λ–dominated cold dark matter (ΛCDM) models, in order to compare with the analytical model of Sheth and van de Weygaert (SvdW) for void statistics. For the subsample of five dark matter simulations in the ΛCDM cosmology with box sizes ranging from 1000h−1Mpc to 8 h−1Mpc, we find that the standard void–in–cloud effect is too simplified to explain several properties of identified small voids in simulations. (i) The number density of voids is found to be larger than the prediction of the analytical model up to 2 orders of magnitude below 1h−1Mpc scales. The Press-Schechter model with the linear critical threshold of void δv = −2.71, or a naive power law, is found to provide an excellent agreement with the void size function, suggesting that the void-in-cloud effect does not suppress as much voids as predicted by the SvdW model. (ii) We then measured the density and velocity profiles of small voids, and find that they are mostly partially collapsing underdensities, instead of being completely crushed in the standard void–in–cloud scenario. (iii) Finally, we measure the void distributions in four different tidal environments, and find that the void–in-void effect alone can explain the correlation between distribution and environments, whereas the void–in–cloud effect is only weakly influencing the abundance of voids, even in filaments and clusters.
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