Dynamical modelling of the twisted galaxy PGC 046832
  We analyse VLT/MUSE observations of PGC 046832, the brightest cluster galaxy
of Abell 3556. The velocity structure of this galaxy is startling and shows two
reversals in sign along the minor axis, and one along the major axis. We use
triaxial Schwarzschild models to infer the intrinsic shape, central black hole
mass and orbit distribution of this galaxy. The shape determination suggests
that the galaxy is highly triaxial in the centre (almost prolate) but has a low
triaxiality (almost oblate) in the outer parts. The orbit distribution of the
best-fit Schwarzschild model shows that the kinematic reversal along the
projected minor axis is driven by a slight asymmetry in the distribution and
amount of long axis tubes in the inner parts. The kinematic reversals along the
projected major axis are driven by a high fraction of counter-rotating orbits
at intermediate radii in the galaxy. Using chemical tagging of orbits in the
Schwarzschild model, we do not find evidence for any association of these
orbits with specific stellar population parameters. Although the inner part of
the galaxy almost certainty formed through one or more dry mergers producing
the prolate shape, the outer parts are consistent with both accretion and in
situ formation. While axisymmetric models suggests the presence of a
supermassive black hole with mass $\sim 6 \times 10^9$M$_{\odot}$ and $\sim
10^{10}$M$_{\odot}$ (with Schwarzschild and Jeans modelling, resp), triaxial
Schwarzschild models provide only an upper limit of $\sim 2 \times
10^9$M$_{\odot}$.
