Heesen, V.Wiegert, T.Irwin, J.Crocker, R.Kiehn, A.Li, J. T.Wang, Q. D.Stein, M.Dettmar, R. J.Soida, M.Henriksen, R.Gajoviać, L.Yang, Y.Brüggen, M.2025-05-232025-05-230004-6361ORCID:/0000-0002-2036-2426/work/184102979http://www.scopus.com/inward/record.url?scp=85210302339&partnerID=8YFLogxKhttps://hdl.handle.net/1885/733751906Context. Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider's view of radio haloes, and of their extra-planar cosmic-ray electrons and magnetic fields. Aims. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC 4217. We examine the distribution of extra-planar cosmic rays and magnetic fields. We observed it with both the Jansky Very Large Array (JVLA) in the S band (2-4 GHz) and the LOw Frequency ARray (LOFAR) at 144 MHz. Methods. We measured vertical intensity profiles and exponential scale heights. We re-imaged both the JVLA and LOFAR data at matched angular resolution in order to measure radio spectral indices between 144 MHz and 3 GHz. Confusing point-like sources were subtracted prior to imaging. We then fitted intensity profiles with cosmic-ray electron advection models, using an isothermal wind model that is driven by a combination of pressure from the hot gas and cosmic rays. Results. We discover a large-scale radio halo on the north-western side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20 kpc from the disc. We find spectral ageing in the bubble, which allowed us to measure the advection speeds of the cosmic-ray electrons, which accelerate from 300 to 600kms-1. Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble may have been inflated by a modest 10% of the kinetic energy injected by supernovae over its dynamical timescale of 35 Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Conclusions. Non-thermal bubbles with sizes of tens of kiloparsecs may be a ubiquitous feature of star-forming galaxies, and if so this would demonstrate the influence of feedback. Determining possible contributions by AGN feedback will require deeper observations.We thank the referee for a constructive report which helped to improve the paper. This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation grant PHY-2210452. We thank Rainer Beck for valuable comments on an early draft of the manuscript. This paper is based (in part) 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 observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Universit\u00E9 d\u2019Orl\u00E9ans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland. TW acknowledges financial support from the grant CEX2021-001131-S funded by MICIU/AEI/ 10.13039/501100011033, from the coordination of the participation in SKA-SPAIN, funded by the Ministry of Science, Innovation and Universities (MICIU). MS and RJD acknowledge funding from the German Science Foundation DFG, within the Collaborative Research Center SFB1491 \u201CCosmic Interacting Matters \u2013 From Source to Signal\u201D. MB acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany\u2019s Excellence Strategy \u2014 EXC 2121 \u201CQuantum Universe\u201D 390833306. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The following software packages have been used in this work: Astropy (Astropy Collaboration 2013, 2018). This research has made use of \u201CAladin sky atlas\u201D developed at CDS, Strasbourg Observatory, France (Bonnarel et al. 2000; Boch & Fernique 2014); SAOImage DS9 (Joye & Mandel 2003). This work made use of the SciPy project https://scipy.org . paper. This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation grant PHY- 2210452. We thank Rainer Beck for valuable comments on an early draft of the manuscript. This paper is based (in part) 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 observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Universit? d'Orl'ans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland. TW acknowledges financial support from the grant CEX2021-001131- S funded by MICIU/AEI/ 10.13039/501100011033, from the coordination of the participation in SKA-SPAIN, funded by the Ministry of Science, Innovation and Universities (MICIU). MS and RJD acknowledge funding from the German Science Foundation DFG, within the Collaborative Research Center SFB1491 'Cosmic Interacting Matters ' From Source to Signal'. MB acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy ' EXC 2121 'Quantum Universe' 390833306. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The following software packages have been used in this work: Astropy (Astropy Collaboration 2013, 2018). This research has made use of 'Aladin sky atlas' developed at CDS, Strasbourg Observatory, France (Bonnarel et al. 2000; Boch & Fernique 2014); SAOImage DS9 (Joye & Mandel 2003). This work made use of the SciPy project https://scipy.org.enPublisher Copyright: © The Authors 2024.Cosmic raysGalaxies: fundamental parametersGalaxies: magnetic fieldsGalaxies: star formationRadio continuum: galaxies2024-11-0110.1051/0004-6361/20245156985210302339