Dominant dark matter and a counter rotating disc: MUSE view of the low
  luminosity S0 galaxy NGC 5102
  The kinematics and stellar populations of the low-mass nearby S0 galaxy NGC
5102 are studied from integral field spectra taken with the Multi-Unit
Spectroscopic Explorer (MUSE). The kinematic maps reveal for the first time
that NGC 5102 has the characteristic 2 sigma peaks indicative of galaxies with
counter-rotating discs. This interpretation is quantitatively confirmed by
fitting two kinematic components to the observed spectra. Through stellar
population analysis we confirm the known young stellar population in the centre
and find steep age and metallicity gradients. We construct axisymmetric Jeans
anisotropic models of the stellar dynamics to investigate the initial mass
function (IMF) and the dark matter halo of the galaxy. The models show that
this galaxy is quite different from all galaxies previously studied with a
similar approach: even within the half-light radius, it cannot be approximated
with the self-consistent mass-follows-light assumption. Including an NFW dark
matter halo, we need a heavy IMF and a dark matter fraction of 0.37+-0.04
within a sphere of one effective radius to describe the stellar kinematics. The
more general model with a free slope of the dark matter halo shows that slope
and IMF are degenerate, but indicates that a light weight IMF (Chabrier-like)
and a higher dark matter fraction, with a steeper (contracted) halo, fit the
data better. Regardless of the assumptions about the halo profile, we measure
the slope of the total mass density to be -1.75+-0.04. This is shallower than
the slope of -2 of an isothermal halo and shallower than published slopes for
more massive early type galaxies.
