The Spectral Energy Distribution of Powerful Starburst Galaxies I : Modelling the Radio Continuum
We have acquired radio-continuum data between 70MHz and 48 GHz for a sample of 19 southern starburst galaxies at moderate redshifts (0.067 < z < 0.227) with the aim of separating synchrotron and free-free emission components. Using a Bayesian framework, we find the radio continuum is rarely characterized well by a single power law, instead often exhibiting lowfrequency turnovers below 500 MHz, steepening at mid to high frequencies, and a flattening at high frequencies where free-free emission begins to dominate over the synchrotron emission. These higher order curvature components may be attributed to free-free absorption across multiple regions of star formation with varying optical depths. The decomposed synchrotron and free-free emission components in our sample of galaxies form strong correlations with the total-infrared bolometric luminosities. Finally, we find that without accounting for free-free absorption with turnovers between 90 and 500MHz the radio continuum at low frequency (v < 200 MHz) could be overestimated by upwards of a factor of 12 if a simple power-law extrapolation is used from higher frequencies. The mean synchrotron spectral index of our sample is constrained to be α = -1.06, which is steeper than the canonical value of -0.8 for normal galaxies. We suggest this may be caused by an intrinsically steeper cosmic ray distribution.
Item Type | Article |
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Uncontrolled Keywords | Galaxies: starburst; Radio continuum: galaxies |
Subjects |
Physics and Astronomy(all) > Astronomy and Astrophysics Earth and Planetary Sciences(all) > Space and Planetary Science |
Date Deposited | 26 Jul 2024 12:11 |
Last Modified | 26 Jul 2024 12:11 |
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Read more research from the creator(s):
- Galvin, T J
- Seymour, N.
- Marvil, J.
- Filipovic, M D
- Tothill, N.F.H.
- McDermid, Richard M.
- Hurley-Walker, N.
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- Callingham, J. R.
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- Norris, Ray P.
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- Gaensler, B. M.
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- Lenc, E.
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- Morgan, J
- Offringa, A. R.
- Procopio, P.
- Staveley-Smith, L.
- Wayth, R. B.
- Wu, C.
- Zheng, Q.
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