The Subhalo Mass Function and Ultralight Bosonic Dark Matter
  Warm dark matter has recently become increasingly constrained by
observational inferences about the low-mass end of the subhalo mass function,
which would be suppressed by dark matter free streaming in the early Universe.
In this work, we point out that a constraint can be placed on ultralight
bosonic dark matter (often referred to as "fuzzy dark matter") based on similar
considerations. Recent limits on warm dark matter from strong gravitational
lensing of quasars and from fluctuations in stellar streams separately
translate to a lower limit of $\sim 2.1 \times 10^{-21}$ eV on the mass of an
ultralight boson comprising all dark matter. These limits are complementary to
constraints on ultralight dark matter from the Lyman-$\alpha$ forest and are
subject to a completely different set of assumptions and systematic
uncertainties. Taken together, these probes strongly suggest that dark matter
with a mass $\sim 10^{-22}$ eV is not a viable way to reconcile differences
between cold dark matter simulations and observations of structure on small
scales.
