The diversity of rotation curves of simulated galaxies with cusps and
  cores
  We use $\Lambda$CDM cosmological hydrodynamical simulations to explore the
kinematics of gaseous discs in late-type dwarf galaxies. We create
high-resolution 21-cm 'observations' of simulated dwarfs produced in two
variations of the EAGLE galaxy formation model: one where supernova-driven gas
flows redistribute dark matter through gravitational interaction and form
constant-density central 'cores', and another where the central 'cusps' survive
intact. We 'observe' each galaxy along multiple sight lines and derive a
rotation curve for each observation using a conventional tilted-ring approach
to model the gas kinematics. We find that the modelling process introduces
systematic discrepancies between the recovered rotation curve and the actual
circular velocity curve driven primarily by (i) non-circular gas orbits within
the discs; (ii) the finite thickness of gaseous discs, which leads to overlap
of different radii in projection; and (iii) departures from dynamical
equilibrium. Dwarfs with dark matter cusps often appear to have a core, whilst
the inverse error is less common. These effects naturally reproduce an observed
trend which other models struggle to explain: late-type dwarfs with more
steeply-rising rotation curves appear to be dark matter-dominated in the inner
regions, whereas the opposite seems to hold in galaxies with core-like rotation
curves. We conclude that if similar effects affect the rotation curves of
observed dwarfs, a late-type dwarf population in which all galaxies have
sizeable dark matter cores is most likely incompatible with current
measurements.
