Despite the progress that has been made in understanding radio relics, there are still open questions regarding the underlying particle acceleration mechanisms. In this paper, we present deep 1-4 GHz Very Large Array (VLA) observations of CIZA J2242.8+5301 (z = 0.1921), a double radio relic cluster characterized by small projection on the plane of the sky. Our VLA observations reveal, for the first time, the complex morphology of the diffuse sources and the filamentary structure of the northern relic. We discover new, faint, diffuse radio emission extending north of the main northern relic. Our Mach number estimates for the northern and southern relics, based on the radio spectral index map obtained using the VLA observations and existing LOw Frequency ARray (LOFAR) and Giant Metrewave Radio Telescope data, are consistent with previous radio and X-ray studies (MRN = 2.58 ± 0.17 and MRS = 2.10 ± 0.08). However, color-color diagrams and models suggest a flatter injection spectral index than the one obtained from the spectral index map, indicating that projection effects might be not entirely negligible. The southern relic consists of five "arms." Embedded in it, we find a tailed radio galaxy that seems to be connected to the relic. A spectral index flattening, where the radio tail connects to the relic, is also measured. We propose that the southern relic may trace AGN fossil electrons that are reaccelerated by a shock, with an estimated strength of M = 2.4. High-resolution mapping of other tailed radio galaxies also supports a scenario where AGN fossil electrons are revived by the merger event and could be related to the formation of some diffuse cluster radio emission.
Bibliographical noteFunding Information:
This work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. R.J.vW. and H.J.A.R. acknowledge support from the ERC Advanced Investigator programme NewClusters 321271. R.J.vW. acknowledges the support of the VIDI research programme under project number 639.042.729, which is financed by the Netherlands Organisation for Scientific Research (NWO). H.K. and D.R. were supported by the NRF of Korea through grants 2016R1A5A1013277, 2017R1A2A1A05071429, and 2017R1D1A1A09000567.
We thank the anonymous referee for useful comments that have improved the quality of the manuscript. This paper is partly based on data obtained with the International LOFAR Telescope (ILT). LOFAR (van Haarlem et al. 2013) is the Low-Frequency Array designed and constructed by ASTRON. It has facilities that are hosted by several countries, owned by various parties (each with their own funding sources), and collectively operated by the ILT foundation under a joint scientific policy. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. R.J.vW. and H.J.A.R. acknowledge support from the ERC Advanced Investigator programme NewClusters 321271. R.J.vW. acknowledges the support of the VIDI research programme under project number 639.042.729, which is financed by the Netherlands Organisation for Scientific Research (NWO). H.K. and D.R. were supported by the NRF of Korea through grants 2016R1A5A1013277, 2017R1A2A1A05071429, and 2017R1D1A1A09000567. We thank the staff of the GMRT for making these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO6-17113X, issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. This research made use of APLpy, an open-source plotting package for Python (Robitaille & Bressert 2012).
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- galaxies: clusters: individual (CIZA J2242.8+5301)