Scalar Field Dark Matter: Helping or Hurting Small-Scale Problems in
  Cosmology?
  Building upon results of cosmological simulations of ultra-light scalar field
dark matter (SFDM), we present a comprehensive model for the density profiles
of SFDM haloes as a function of halo virial mass $M_{\rm h}$ and scalar field
mass $m$. The central regions of SFDM haloes are dominated by solitons with
characteristic densities that increase with increasing halo mass and asymptote
to CDM-like profiles at large radii. For scalar field masses $m \sim 10^{-22}$
eV, consistent with large-scale structure observations, $M_{\rm h} \sim 10^{10}
\,M_\odot$ haloes have lower core densities than their Cold Dark Matter (CDM)
counterparts and this alleviates the Too Big to Fail problem (TBTF) in a regime
where feedback is less effective. However, higher-mass SFDM haloes with $M_{\rm
h} \sim 10^{11} \,M_\odot$ are denser than their CDM counterparts at small,
observationally relevant radii. We use rotation curves of $V \sim 100$ km
s$^{-1}$ galaxies from the SPARC database to show that SFDM exacerbates the
cusp/core and central density problems seen in CDM at this scale. We conclude
that if the conventional cosmological SFDM scaling relations are correct, then
baryonic feedback is required to lower densities in SFDM haloes even more so
than in CDM. This motivates cosmological and self-consistent hydrodynamic
simulations of SFDM to determine whether central soliton structure can be
altered by realistic feedback implementations.
