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The Merging Galaxy Cluster A520 - A Broken-Up Cool Core, A Dark Subcluster, and an X-Ray ChannelWe present results from a deep Chandra X-ray observation of a merging galaxy cluster A520. A high-resolution gas temperature map reveals a long trail of dense, cool clumpsapparently the fragments of a cool core that has been stripped from the infalling subcluster by ram pressure. The clumps should still be connected by the stretched magnetic field lines. The observed temperature variations imply that thermal conductivity is suppressed by a factor greater than 100 across the presumed direction of the magnetic field (as found in other clusters), and is also suppressed along the field lines by a factor of several. Two massive clumps in the periphery of A520, visible in the weak-lensing mass map and the X-ray image, have apparently been completely stripped of gas during the merger, but then re-accreted the surrounding high-entropy gas upon exit from the cluster. The mass clump that hosted the stripped cool core is also re-accreting hotter gas. An X-ray hydrostatic mass estimate for the clump that has the simplest geometry agrees with the lensing mass. Its current gas mass to total mass ratio is very low, 1.5 percent to 3 percent, which makes it a "dark subcluster." We also found a curious low X-ray brightness channel (likely a low-density sheet in projection) going across the cluster along the direction of an apparent secondary merger. The channel may be caused by plasma depletion in a region of an amplified magnetic field (with plasma Beta approximately equal to 10-20). The shock in A520 will be studied in a separate paper.
Document ID
Document Type
Reprint (Version printed in journal)
Wang, Qian H.S. (Maryland Univ. College Park, MD, United States)
Markevitch, Maxim (NASA Goddard Space Flight Center Greenbelt, MD United States)
Giacintucci, Simona (Maryland Univ. College Park, MD, United States)
Date Acquired
July 6, 2017
Publication Date
December 9, 2016
Publication Information
Publication: The Astrophysical Journal
Volume: 833
Issue: 1
ISSN: 2041-8205
Subject Category
Report/Patent Number
Funding Number(s)
CONTRACT_GRANT: Chandra GO3-14144Z
CONTRACT_GRANT: Chandra GO5-16147Z
Distribution Limits
galaxies: clusters: individual (A520) – intergalactic medium – X-rays: galax