Galactic disc heating by density granulation in fuzzy dark matter simulations
Journal
Monthly Notices of the Royal Astronomical Society
Journal Volume
530
Journal Issue
1
Start Page
129
End Page
148
ISSN
0035-8711
1365-2966
Date Issued
2024-03-30
Author(s)
Abstract
Fuzzy dark matter (FDM), an attractive dark matter candidate comprising ultralight bosons (axions) with a particle mass m a ∼10 -22 eV, is moti v ated by the small-scale challenges of cold dark matter and features a kpc-size de Broglie wavelength. Quantum wave interference inside an FDM halo gives rise to stochastically fluctuating density granulation; the resulting gravitational perturbations could drive significant disc thickening, providing a natural explanation for galactic thick discs. Here we present the first self-consistent simulations of FDM haloes and stellar discs, exploring m a = 0.2-1.2 ×10 -22 eV and halo masses M h = 0.7-2.8 ×10 11 M ⊙. Disc thickening is observed in all simulated systems. The disc heating rates are approximately constant in time and increase substantially with decreasing m a , reaching d h /d t ≃ 0.04 (0.4) kpc Gyr -1 and d σ2 z / d t ≃ 4 (150) km 2 s -2 Gyr -1 for m a = 1.2 (0.2) ×10 -22 eV and M h = 7 ×10 10 M ⊙, where h is the disc scale height and σz is the vertical velocity dispersion. These simulated heating rates agree within a factor of two with the theoretical estimates of Chiang et al., confirming that the rough estimate of Church et al. o v erpredicts the granulation-driv en disc heating rate by two orders of magnitude. Ho we ver, the simulation-inferred heating rates scale less steeply than the theoretically predicted relation d σ2 z / d t ∝ m -3 a . Finally, we examine the applicability of the Fokker-Planck approximation in FDM granulation modelling and the robustness of the m a exclusion bound derived from the Galactic disc kinematics.
Subjects
dark matter
galaxies: haloes
galaxies: kinematics and dynamics
galaxies: structure
methods: numerical
Publisher
Oxford University Press (OUP)
Type
journal article