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Title: The case for electron re-acceleration at galaxy cluster shocks

On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found. Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster–cluster merger events. A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411–3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. Lastly, it also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ORCiD logo [6] ;  [7] ;  [8] ;  [1] ;  [1] ; ORCiD logo [9] ; ORCiD logo [10] ;  [11] ;  [12] ;  [1] ; ORCiD logo [13] ;  [14] ;  [15]
  1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Univ. of California, Davis, CA (United States)
  4. National Centre for Radio Astrophysics, Pune (India)
  5. Pusan National Univ., Busan (Korea, Republic of). Dept. of Earth Sciences
  6. Ulsan National Inst. of Science and Technology (UNIST), Ulsan (Korea). Dept. of Physics; Korea Astronomy and Space Science Inst., Daejeon (Korea)
  7. Hamburg Univ., Hamburg (Germany). Hamburger Sternwarte
  8. Stanford Univ., CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
  9. Univ. of Notre Dame, IN (United States). Dept. of Physics and JINA Center for the Evolution of the Elements
  10. Univ. de Sao Paulo, Sao Paulo (Brazil). Dept. de Astronomia - Instituto de Astronomia, Geofisica e Ciencias Atmosfericas
  11. Univ. of California, Davis, CA (United States); Univ. de Lisboa, Lisbon (Portugal). Instituto de Astrofisica e Ciencias do Espaco
  12. Yonsei Univ., Seoul (Korea). Dept. of Astronomy and Center for Galaxy Evolution Research
  13. Lancaster Univ. (United Kingdom). Dept. of Physics; Leiden Univ. (Netherlands). Leiden Observatory
  14. European Southern Observatory, Garching (Germany)
  15. Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
Publication Date:
Report Number(s):
LLNL-JRNL-703259
Journal ID: ISSN 2397-3366
Grant/Contract Number:
AC52-07NA27344; NAS8-03060; 2016R1A5A1013277; 2014R1A1A2057940; HST-HF2-51345.001-A; NAS5-26555
Type:
Accepted Manuscript
Journal Name:
Nature Astronomy
Additional Journal Information:
Journal Volume: 1; Journal Issue: 1; Journal ID: ISSN 2397-3366
Publisher:
Springer
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE; National Aeronautic and Space Administration (NASA); National Research Foundation of Korea (NRF)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1430992

van Weeren, Reinout J., Andrade-Santos, Felipe, Dawson, William A., Golovich, Nathan, Lal, Dharam V., Kang, Hyesung, Ryu, Dongsu, Bruggen, Marcus, Ogrean, Georgiana A., Forman, William R., Jones, Christine, Placco, Vinicius M., Santucci, Rafael M., Wittman, David, Jee, M. James, Kraft, Ralph P., Sobral, David, Stroe, Andra, and Fogarty, Kevin. The case for electron re-acceleration at galaxy cluster shocks. United States: N. p., Web. doi:10.1038/s41550-016-0005.
van Weeren, Reinout J., Andrade-Santos, Felipe, Dawson, William A., Golovich, Nathan, Lal, Dharam V., Kang, Hyesung, Ryu, Dongsu, Bruggen, Marcus, Ogrean, Georgiana A., Forman, William R., Jones, Christine, Placco, Vinicius M., Santucci, Rafael M., Wittman, David, Jee, M. James, Kraft, Ralph P., Sobral, David, Stroe, Andra, & Fogarty, Kevin. The case for electron re-acceleration at galaxy cluster shocks. United States. doi:10.1038/s41550-016-0005.
van Weeren, Reinout J., Andrade-Santos, Felipe, Dawson, William A., Golovich, Nathan, Lal, Dharam V., Kang, Hyesung, Ryu, Dongsu, Bruggen, Marcus, Ogrean, Georgiana A., Forman, William R., Jones, Christine, Placco, Vinicius M., Santucci, Rafael M., Wittman, David, Jee, M. James, Kraft, Ralph P., Sobral, David, Stroe, Andra, and Fogarty, Kevin. 2017. "The case for electron re-acceleration at galaxy cluster shocks". United States. doi:10.1038/s41550-016-0005. https://www.osti.gov/servlets/purl/1430992.
@article{osti_1430992,
title = {The case for electron re-acceleration at galaxy cluster shocks},
author = {van Weeren, Reinout J. and Andrade-Santos, Felipe and Dawson, William A. and Golovich, Nathan and Lal, Dharam V. and Kang, Hyesung and Ryu, Dongsu and Bruggen, Marcus and Ogrean, Georgiana A. and Forman, William R. and Jones, Christine and Placco, Vinicius M. and Santucci, Rafael M. and Wittman, David and Jee, M. James and Kraft, Ralph P. and Sobral, David and Stroe, Andra and Fogarty, Kevin},
abstractNote = {On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found. Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster–cluster merger events. A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411–3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. Lastly, it also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.},
doi = {10.1038/s41550-016-0005},
journal = {Nature Astronomy},
number = 1,
volume = 1,
place = {United States},
year = {2017},
month = {1}
}