Dark matter dynamics in Abell 3827: new data consistent with standard
  Cold Dark Matter
  We present integral field spectroscopy of galaxy cluster Abell 3827, using
ALMA and VLT/MUSE. It reveals an unusual configuration of strong gravitational
lensing in the cluster core, with at least seven lensed images of a single
background spiral galaxy. Lens modelling based on HST imaging had suggested
that the dark matter associated with one of the cluster's central galaxies may
be offset. The new spectroscopic data enable better subtraction of foreground
light, and better identification of multiple background images. The inferred
distribution of dark matter is consistent with being centered on the galaxies,
as expected by LCDM. Each galaxy's dark matter also appears to be symmetric.
Whilst we do not find an offset between mass and light (suggestive of
self-interacting dark matter) as previously reported, the numerical simulations
that have been performed to calibrate Abell 3827 indicate that offsets and
asymmetry are still worth looking for in collisions with particular geometries.
Meanwhile, ALMA proves exceptionally useful for strong lens image
identifications.
