CHANG-ES XXXIV: a 20 kpc radio bubble in the halo of the star-forming galaxy NGC 4217
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arXiv
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| Autori principali: | , , , , , , , , , , , , , |
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| Natura: | Preprint |
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2024
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| author | 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. Gajovic, L. Yang, Y. Brüggen, M. |
| author_facet | 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. Gajovic, L. Yang, Y. Brüggen, M. |
| contents | Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider's view of the radio halo, which shows the presence of extra-planar cosmic-ray electrons and magnetic fields. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC 4217 in order to study the distribution of extra-planar cosmic rays and magnetic fields. We both observe with the Jansky Very Large Array (JVLA) in the S-band (2-4 GHz) and with LOw Frequency ARray (LOFAR) at 144 MHz. We measure vertical intensity profiles and exponential scale heights. We re-image both 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. Intensity profiles are then fitted with cosmic-ray electron advection models, where we use an isothermal wind model that is driven by a combination of pressure from the hot gas and cosmic rays. We discover a large-scale radio halo on one (northwestern) side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20 kpc away from the disc. We find spectral ageing in the bubble which allows us to measure advection speeds of the cosmic-ray electrons accelerating from 300 to 600 $\rm km\, s^{-1}$ . Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble can be inflated by a modest 10 per cent of the kinetic energy injected by supernovae over its dynamical time-scale of 35 Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Non-thermal bubbles with sizes of tens of kiloparsec may be a ubiquitous feature of star-forming galaxies showing the influence of feedback. To determine possible contributions by AGN feedback, will require deeper observations. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2409_15449 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | CHANG-ES XXXIV: a 20 kpc radio bubble in the halo of the star-forming galaxy NGC 4217 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. Gajovic, L. Yang, Y. Brüggen, M. Astrophysics of Galaxies Cosmic rays may be dynamically very important in driving large-scale galactic winds. Edge-on galaxies give us an outsider's view of the radio halo, which shows the presence of extra-planar cosmic-ray electrons and magnetic fields. We present a new radio continuum imaging study of the nearby edge-on galaxy NGC 4217 in order to study the distribution of extra-planar cosmic rays and magnetic fields. We both observe with the Jansky Very Large Array (JVLA) in the S-band (2-4 GHz) and with LOw Frequency ARray (LOFAR) at 144 MHz. We measure vertical intensity profiles and exponential scale heights. We re-image both 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. Intensity profiles are then fitted with cosmic-ray electron advection models, where we use an isothermal wind model that is driven by a combination of pressure from the hot gas and cosmic rays. We discover a large-scale radio halo on one (northwestern) side of the galactic disc. The morphology is reminiscent of a bubble extending up to 20 kpc away from the disc. We find spectral ageing in the bubble which allows us to measure advection speeds of the cosmic-ray electrons accelerating from 300 to 600 $\rm km\, s^{-1}$ . Assuming energy equipartition between the cosmic rays and the magnetic field, we estimate the bubble can be inflated by a modest 10 per cent of the kinetic energy injected by supernovae over its dynamical time-scale of 35 Myr. While no active galactic nucleus (AGN) has been detected, such activity in the recent past cannot be ruled out. Non-thermal bubbles with sizes of tens of kiloparsec may be a ubiquitous feature of star-forming galaxies showing the influence of feedback. To determine possible contributions by AGN feedback, will require deeper observations. |
| title | CHANG-ES XXXIV: a 20 kpc radio bubble in the halo of the star-forming galaxy NGC 4217 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2409.15449 |