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Pandora's Cluster
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Pandora's Cluster - A galactic crash investigation

A team of scientists has studied the galaxy cluster Abell 2744, nicknamed Pandora's Cluster. They have pieced together the cluster's complex and violent history using telescopes in space and on the ground, including the Hubble Space Telescope and ESO's Very Large Telescope. Abell 2744 seems to be the result of a simultaneous pile-up of at least four separate galaxy clusters and this complex collision has produced strange effects that have never been seen together before.
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Posts: 131433
Date:
Abell 2744
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Title: Creation of cosmic structure in the complex galaxy cluster merger Abell 2744
Authors: J. Merten, D. Coe, R. Dupke, R. Massey, A. Zitrin, E.S. Cypriano, N. Okabe, B. Frye, F. Braglia, Y. Jimenez-Teja, N. Benitez, T. Broadhurst, J. Rhodes, M. Meneghetti, L.A. Moustakas, L. Sodre Jr., J. Krick, J.N. Bregman

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. We dub the system Pandora's Cluster, because 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 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 nearly 500 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.

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