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Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301

Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301
Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301
CIZA J2242.8+5301, a merging galaxy cluster at z = 0.19, hosts a double-relic system and a faint radio halo. Radio observations at frequencies ranging from a few MHz to several GHz have shown that the radio spectral index at the outer edge of the northern relic corresponds to a shock of Mach number 4.6+1.3?0.9, under the assumptions of diffusive shock acceleration of thermal particles in the test-particle regime. Here, we present results from new Chandra observations of the cluster. The Chandra surface brightness profile across the northern relic only hints to a surface brightness discontinuity (<2? detection). Nevertheless, our reanalysis of archival Suzaku data indicates a temperature discontinuity across the relic that is consistent with a Mach number of 2.54+0.64?0.43, in agreement with previously published results. This confirms that the Mach number at the shock traced by the northern relic is much weaker than predicted from the radio. Puzzlingly, in the Chandra data we also identify additional inner small density discontinuities both on and off the merger axis. Temperature measurements on both sides of the discontinuities do not allow us to undoubtedly determine their nature, although a shock front interpretation seems more likely. We speculate that if the inner density discontinuities are indeed shock fronts, then they are the consequence of violent relaxation of the dark matter cores of the clusters involved in the merger.
1365-2966
3416-3425
Ogrean, G.A.
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Bruggen, M.
ceb564a4-72c5-460f-9081-1a86a5af575e
van Weeren, R.
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Rottgering, H.
c041ac34-0c57-45a7-b294-3805fed6adbb
Simionescu, A.
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Hoeft, M.
d5578132-2074-48dd-b634-cdb028ab86ab
Croston, J.H.
b10aa3fb-620e-4ec2-93e5-8594748d4822
Ogrean, G.A.
d75122b2-8708-4751-8d09-bf9ed6b348f3
Bruggen, M.
ceb564a4-72c5-460f-9081-1a86a5af575e
van Weeren, R.
952dcd5c-ffcd-4a9e-8a56-1881bf407049
Rottgering, H.
c041ac34-0c57-45a7-b294-3805fed6adbb
Simionescu, A.
30e9028f-ca44-4985-a17f-324a0bf1af72
Hoeft, M.
d5578132-2074-48dd-b634-cdb028ab86ab
Croston, J.H.
b10aa3fb-620e-4ec2-93e5-8594748d4822

Ogrean, G.A., Bruggen, M., van Weeren, R., Rottgering, H., Simionescu, A., Hoeft, M. and Croston, J.H. (2014) Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301. Monthly Notices of the Royal Astronomical Society, 440 (4), 3416-3425, [stu537]. (doi:10.1093/mnras/stu537).

Record type: Article

Abstract

CIZA J2242.8+5301, a merging galaxy cluster at z = 0.19, hosts a double-relic system and a faint radio halo. Radio observations at frequencies ranging from a few MHz to several GHz have shown that the radio spectral index at the outer edge of the northern relic corresponds to a shock of Mach number 4.6+1.3?0.9, under the assumptions of diffusive shock acceleration of thermal particles in the test-particle regime. Here, we present results from new Chandra observations of the cluster. The Chandra surface brightness profile across the northern relic only hints to a surface brightness discontinuity (<2? detection). Nevertheless, our reanalysis of archival Suzaku data indicates a temperature discontinuity across the relic that is consistent with a Mach number of 2.54+0.64?0.43, in agreement with previously published results. This confirms that the Mach number at the shock traced by the northern relic is much weaker than predicted from the radio. Puzzlingly, in the Chandra data we also identify additional inner small density discontinuities both on and off the merger axis. Temperature measurements on both sides of the discontinuities do not allow us to undoubtedly determine their nature, although a shock front interpretation seems more likely. We speculate that if the inner density discontinuities are indeed shock fronts, then they are the consequence of violent relaxation of the dark matter cores of the clusters involved in the merger.

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Accepted/In Press date: 14 March 2014
e-pub ahead of print date: 17 April 2014
Published date: 1 June 2014
Organisations: Astronomy Group

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Local EPrints ID: 401982
URI: http://eprints.soton.ac.uk/id/eprint/401982
ISSN: 1365-2966
PURE UUID: 34a37f0f-a1bb-42c7-bed6-25a0baffda1f

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Date deposited: 26 Oct 2016 13:08
Last modified: 15 Mar 2024 03:03

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Contributors

Author: G.A. Ogrean
Author: M. Bruggen
Author: R. van Weeren
Author: H. Rottgering
Author: A. Simionescu
Author: M. Hoeft
Author: J.H. Croston

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