Creation of cosmic structure in the complex galaxy cluster merger Abell
  2744
  We present a detailed strong lensing, weak lensing and X-ray analysis of
Abell 2744 (z = 0.308), one of the most actively merging galaxy clusters known.
It appears to have unleashed `dark', `ghost', `bullet' and `stripped'
substructures, each ~10^14 solar masses. The phenomenology is complex and will
present a challenge for numerical simulations to reproduce. With new, multiband
HST imaging, we identify 34 strongly-lensed images of 11 galaxies around the
massive Southern `core'. Combining this with weak lensing data from HST, VLT
and Subaru, we produce the most detailed mass map of this cluster to date. We
also perform an independent analysis of archival Chandra X-ray imaging. Our
analyses support a recent claim that the Southern core and Northwestern
substructure are post-merger and exhibit morphology similar to the Bullet
Cluster viewed from an angle. From the separation between X-ray emitting gas
and lensing mass in the Southern core, we derive a new and independent
constraint on the self-interaction cross section of dark matter particles
sigma/m <~ 3 \pm 1 cm^2 g^-1. In the Northwestern substructure, the gas, dark
matter, and galaxy components have become separated by much larger distances.
Most curiously, the `ghost' clump (primarily gas) leads the `dark' clump
(primarily dark matter) by more than 150 kpc. We propose an enhanced
`ram-pressure slingshot' scenario which may have yielded this reversal of
components with such a large separation, but needs further confirmation by
follow-up observations and numerical simulations. A secondary merger involves a
second `bullet' clump in the North and an extremely `stripped' clump to the
West. The latter appears to exhibit the largest separation between dark matter
and X-ray emitting baryons detected to date in our sky.
