Can ultralight dark matter explain the age-velocity dispersion relation of the Milky Way disc: A revised and improved treatment
Journal
Monthly Notices of the Royal Astronomical Society
Journal Volume
518
Journal Issue
3
Date Issued
2022-11-14
Author(s)
Abstract
Ultralight axion-like particles $m_a \sim 10^{-22}$ eV, or Fuzzy Dark Matter
(FDM), behave comparably to cold dark matter (CDM) on cosmological scales and
exhibit a kpc-size de Broglie wavelength capable of alleviating established
(sub-)galactic-scale problems of CDM. Substructures inside an FDM halo incur
gravitational potential perturbations, resulting in stellar heating sufficient
to account for the Galactic disc thickening over a Hubble time, as first
demonstrated by Church et al. We present a more sophisticated treatment that
incorporates the full baryon and dark matter distributions of the Milky Way and
adopts stellar disc kinematics inferred from recent Gaia, APOGEE, and LAMOST
surveys. Ubiquitous density granulation and subhalo passages respectively drive
inner disc thickening and flaring of the outer disc, resulting in an
observationally consistent `U-shaped' disc vertical velocity dispersion profile
with the global minimum located near the solar radius. The observed
age-velocity dispersion relation in the solar vicinity can be explained by the
FDM-substructure-induced heating and places an exclusion bound $m_a \gtrsim
0.4\times10^{-22}$ eV. We assess non-trivial uncertainties in the empirical
core-halo relation, FDM subhalo mass function and tidal stripping, and stellar
heating estimate. The mass range $m_a\simeq 0.5-0.7\times10^{-22}$ eV favoured
by the observed thick disc kinematics is in tension with several exclusion
bounds inferred from dwarf density profiles, stellar streams, and Milky Way
satellite populations, which could be significantly relaxed due to the
aforesaid uncertainties. Additionally, strongly anisotropic heating could help
explain the formation of ultra-thin disc galaxies.
Subjects
cosmology: theory | dark matter | galaxies: haloes | Galaxy: disc | Galaxy: kinematics and dynamics | Galaxy: structure; astro-ph.GA; astro-ph.GA; astro-ph.CO; High Energy Physics - Phenomenology
Description
19 pages, 9 figures; Accepted for publication in MNRAS. Matches
published version
published version
Type
journal article