Abell 1430: A merging cluster with exceptional diffuse radio emission
Astronomy and Astrophysics, vol. 654, pp. A68
Abstract
Context. Diffuse radio emission has been found in many galaxy clusters, predominantly in massive systems which are in the state of merging. The radio emission can usually be classified as relic or halo emission, which are believed to be related to merger shocks or volume-filling turbulence, respectively. Recent observations have revealed radio bridges for some pairs of very close galaxy clusters. The mechanisms that may allow one to explain the high specific density of relativistic electrons, which are necessary to explain the radio luminosity of these bridge regions, have been poorly explored until now. Aims. When inspecting the first data release of the LOFAR Two-Metre Sky Survey (LoTSS), we discovered diffuse radio emission in the galaxy cluster Abell 1430. Here, we aim to determine the dynamical state of the cluster and characterise the diffuse radio emission. Methods. We analysed the LoTSS data in detail and complemented them with recent Karl G. Jansky Very Large Array observations in the L-band. To study the dynamical state of the cluster, we analysed XMM-Newton data, Chandra data, and Sloan Digital Sky Survey data. Moreover, we compared our results to clusters extracted from THE THREE HUNDRED PROJECT cosmological simulation. Results. We find that Abell 1430 consists of two components, namely A1430-A and A1430-B, with a mass ratio of about 2:1. The massive component shows diffuse radio emission which can be classified as radio halo which shows a low radio power at 1.4 GHz with respect to the mass of the cluster. Most interestingly, there is extended diffuse radio emission in the following dubbed as the ‘Pillow’ according to its morphology, which is apparently related to A1430-B and which is neither typical halo nor typical relic emission. The origin of this emission is puzzling. We speculate that the two components of Abell 1430 undergo an off-axis merger. In this scenario, A1430-B is moving towards the main cluster component and may have compressed and stirred the medium in the filament between the two cluster components. Conclusions. We have discovered evidence for diffuse radio emission related to the low-density intracluster or intergalactic medium in Abell 1430. To date, only a few examples of emission originating from such regions are known. These discoveries are crucial to constrain possible acceleration mechanisms which may allow us to explain the presence of relativistic electrons in these regions. In particular, our results indicate a spectral index of α144 MHz1.5 GHz = −1.4±0.5 for the Pillow. If upcoming observations confirm a slope as flat as −1.4 or even flatter, this would pose a challenge for the electron acceleration scenarios.
Authors 19
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Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Mbarara University of Science and Technology · Thüringer Landessternwarte Tautenburg
Affiliation as printed
Mbarara University of Science & Technology, PO Box 1410 Mbarara, Uganda
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Istituto di Radioastronomia di Bologna · Thüringer Landessternwarte Tautenburg · University of Bologna
Affiliation as printed
Dipartimento di Fisica e Astronomia, Universitá di Bologna, Via P. Gobetti 93/2, 40129 Bologna, Italy
INAF-Istituto di Radio Astronomia, Via Gobetti 101, 40129 Bologna, Italy
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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National Institute for Astrophysics
Affiliation as printed
IASF-Milano, INAF, Via A. Corti 12, 20133 Milano, Italy
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Universidad de Buenos Aires · Institute of Astronomy and Space Physics
Affiliation as printed
Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), CC 67, Suc. 28, 1428 Buenos Aires, Argentina
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands
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Thüringer Landessternwarte Tautenburg
Affiliation as printed
Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands
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Istituto di Radioastronomia di Bologna
Affiliation as printed
INAF-Istituto di Radio Astronomia, Via Gobetti 101, 40129 Bologna, Italy
INAF, Istituto di Radio Astronomia, Via Gobetti 101, 40129 Bologna, Italy
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Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy
Affiliation as printed
ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Istituto di Radioastronomia di Bologna
Affiliation as printed
INAF-Istituto di Radio Astronomia, Via Gobetti 101, 40129 Bologna, Italy
INAF, Istituto di Radio Astronomia, Via Gobetti 101, 40129 Bologna, Italy
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Affiliation as printed
University of Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands
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National Institute for Astrophysics
Affiliation as printed
IASF-Milano, INAF, Via A. Corti 12, 20133 Milano, Italy
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Center for Astrophysics Harvard & Smithsonian · Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
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Universidad Autónoma de Madrid
Affiliation as printed
Departamento de Física Teórica and CIAFF, Módulo 8, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Cantoblanco, Madrid, Spain
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Osservatorio di Astrofisica e Scienza dello Spazio · National Institute for Astrophysics
Affiliation as printed
INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
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Affiliation as printed
Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
Department of Astronomy, University of Geneva, ch. d’ Écogia 16, 1290 Versoix, Switzerland
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