Abell 1430: A merging cluster with exceptional diffuse radio emission

Journal Article · Tue Oct 12 00:00:00 EDT 2021 · Astronomy and Astrophysics

DOI:https://doi.org/10.1051/0004-6361/202039725· OSTI ID:1982272

Hoeft, M. ^[1]; Dumba, C. ^[2]; Drabent, A. ^[1]; Rajpurohit, K. ^[3]; Rossetti, M. ^[4]; Nuza, S. E. ^[5]; van Weeren, R. J. ^[6]; Meusinger, H. ^[1]; Botteon, A. ^[6]; Brunetti, G. ^[7]; Shimwell, T. W. ^[8]; Cassano, R. ^[7]; Brüggen, M. ^[9]; Röttgering, H. A. ^[6]; Gastaldello, F. ^[4]; Lovisari, L. ^[10]; Yepes, G. ^[11]; Andrade-Santos, F. ^[12]; Eckert, D. ^[13]

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1. Karl Schwarzschild Observatory (Germany)
2. Mbarara University of Science & Technology (Uganda); Karl Schwarzschild Observatory (Germany)
3. Univ. of Bologna (Italy); Istituto Nazionale di Astrofisica (INAF), Bologna (Italy); Karl Schwarzschild Observatory (Germany)
4. Istituto Nazionale di Astrofisica (INAF), Milano (Italy)
5. Institute of Astronomy and Space Physics (Argentina); Univ. of Buenos Aires (Argentina)
6. Leiden Univ. (Netherlands)
7. Istituto Nazionale di Astrofisica (INAF), Bologna (Italy)
8. Netherlands Institute for Radio Astronomy (Netherlands); Leiden Univ. (Netherlands)
9. Univ. of Hamburg (Germany)
10. Istituto Nazionale di Astrofisica (INAF), Bologna (Italy). Osservatorio di Astrofisica e Scienza dello Spazio di Bologna (OAS); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
11. Autonomous University of Madrid (Spain)
12. Istituto Nazionale di Astrofisica (INAF), Bologna (Italy). Osservatorio di Astrofisica e Scienza dello Spazio di Bologna (OAS)
13. Univ. of Geneva (Switzerland)

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. 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, for this work, we aim to determine the dynamical state of the cluster and characterise the diffuse radio emission. 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. 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. 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 MHz^{1.5 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.

• Research Organization: US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
• Sponsoring Organization: USDOE; National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); Alfred P. Sloan Foundation
• OSTI ID: 1982272
• Journal Information: Astronomy and Astrophysics, Vol. 654; ISSN 0004-6361
• Publisher: EDP Sciences
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
galaxies
clusters
Abell 1430
non-thermal radiation mechanisms
thermal radiation mechanisms
interferometric techniques
general radio continuum