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Discovery of a Double Radio Relic in ZwCl1447.2+2619: A Rare Testbed for Shock-acceleration Models with a Peculiar Surface-brightness Ratio

Lee, Wonki and Jee, M. James and Finner, Kyle and HyeongHan, Kim and Kale, Ruta and Yoon, Hyein and Forman, William and Kraft, Ralph and Jones, Christine and Chung, Aeree (2022) Discovery of a Double Radio Relic in ZwCl1447.2+2619: A Rare Testbed for Shock-acceleration Models with a Peculiar Surface-brightness Ratio. Astrophysical Journal, 924 (1). Art. No. 18. ISSN 0004-637X. doi:10.3847/1538-4357/ac32c5.

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We report a discovery of a double radio relic in the cluster merger ZwCl1447.2+2619 (z = 0.376) with uGMRT observations at 420 MHz and 700 MHz. The linear sizes of the northern and southern relics are ∼0.3 Mpc and ∼1.2 Mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. However, ZwCl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. In this merger, the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. The surface brightness ratio ∼0.1 between the two radio relics differs significantly from the relation observed in other double radio relic systems. From our radio spectral analysis, we find that both relics signify similar weak shocks with Mach numbers of 2.9 ± 0.8 and 2.0 ± 0.7 for the northern and southern relics, respectively. Moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic-ray injection and reacceleration. Therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with reacceleration of fossil cosmic rays. Our multi-wavelength analysis and numerical simulation suggest that ZwCl1447.2+2619 is a postmerger, which has experienced a near head-on collision ∼0.7 Gyr ago.

Item Type:Article
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URLURL TypeDescription Paper
Lee, Wonki0000-0002-1566-5094
Finner, Kyle0000-0002-4462-0709
HyeongHan, Kim0000-0002-2550-5545
Kale, Ruta0000-0003-1449-3718
Yoon, Hyein0000-0003-4048-2203
Forman, William0000-0002-9478-1682
Kraft, Ralph0000-0002-0765-0511
Chung, Aeree0000-0003-1440-8552
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 September 1; revised 2021 October 15; accepted 2021 October 21; published 2022 January 6. We thank Nathan Golovich for sharing his Keck/DEIMOS optical spectrum data and Juheon Lee and Ishwara Chandra for useful discussions. M.J.J. acknowledges support for the current research from the National Research Foundation (NRF) of Korea under the programs 2017R1A2B2004644 and 2020R1A4A2002885. R.K. acknowledges the support of the Department of Atomic Energy, Government of India under project no. 12-R&D-TFR-5.02-0700. We thank the staff of the GMRT who have made these observations possible. The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
National Research Foundation of Korea2017R1A2B2004644
National Research Foundation of Korea2020R1A4A2002885
Department of Atomic Energy (India)12-R&D-TFR-5.02-0200
Subject Keywords:Galaxy clusters; Radio continuum emission; X-ray astronomy; Weak gravitational lensing; Galaxy spectroscopy
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Galaxy clusters (584); Radio continuum emission (1340); X-ray astronomy (1810); Weak gravitational lensing (1797); Galaxy spectroscopy (2171)
Record Number:CaltechAUTHORS:20220118-993028000
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Official Citation:Wonki Lee et al 2022 ApJ 924 18
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112951
Deposited By: George Porter
Deposited On:19 Jan 2022 16:10
Last Modified:19 Jan 2022 16:10

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