Year: 2024
Type: article
Abstract: Context. 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 600 km s−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.
Authors: V. Heesen, T. Wiegert, J. Irwin, R. Crocker, A. Kiehn, J.-T. Li, Q. D. Wang, M. Stein, R.-J. Dettmar, M. Soida, R. Henriksen, L. Gajović, Y. Yang, M. Brüggen
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Aspen Center for Physics, Ministerio de Ciencia, Innovación y Universidades, Science Foundation Ireland, Deutsche Forschungsgemeinschaft, Bundesministerium für Bildung und Forschung, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Max-Planck-Gesellschaft, Centre National de la Recherche Scientifique, Université d'Orléans, Ministerium für Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen, Jet Propulsion Laboratory, Observatoire de Paris, Université de Recherche Paris Sciences et Lettres, Science and Technology Facilities Council, Agencia Estatal de Investigación
Awards: G1105844351, G1175115578, G2262748287, G2550080368, G2595738051, G300979063, G3480869486, G373897614, G425668148, G432818845, G463062595, G491712853, G5080475149, G5894067328, G702601109, EXC 2121: Quantum Universe, G7518687652, G7805626310, G7863371703, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, G8497050386, G8733234872
OpenAlex ID: W6959188440
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