NIHAO XIV: Reproducing the observed diversity of dwarf galaxy rotation
  curve shapes in LCDM
  The significant diversity of rotation curve (RC) shapes in dwarf galaxies has
recently emerged as a challenge to LCDM: in dark matter (DM) only simulations,
DM halos have a universal cuspy density profile that results in self-similar RC
shapes. We compare RC shapes of simulated galaxies from the NIHAO project with
observed galaxies from the homogeneous SPARC dataset. The DM halos of the NIHAO
galaxies can expand to form cores, with the degree of expansion depending on
their stellar-to-halo mass ratio. By means of the $V_{\rm 2kpc}-V_{\rm Rlast}$
relation (where $V_{\rm Rlast}$ is the outermost measured rotation velocity),
we show that both the average trend and the scatter in RC shapes of NIHAO
galaxies are in reasonable agreement with SPARC: this represents a significant
improvement compared to simulations that do not result in DM core formation,
suggesting that halo expansion is a key process in matching the diversity of
dwarf galaxy RCs. Note that NIHAO galaxies can reproduce even the extremely
slowly rising RCs of IC 2574 and UGC 5750. Revealingly, the range where
observed galaxies show the highest diversity corresponds to the range where
core formation is most efficient in NIHAO simulations, 50$<V_{\rm Rlast}$\km
s$^{-1}<$100. A few observed galaxies in this range cannot be matched by any
NIHAO RC nor by simulations that predict a universal halo profile.
Interestingly, the majority of these are starbursts or emission-line galaxies,
with steep RCs and small effective radii. Such galaxies represent an
interesting observational target providing new clues to the process/viability
of cusp-core transformation, the relationship between starburst and inner
potential well, and the nature of DM.
