LOFAR total-intensity surveys of nearby galaxies
Final Report Abstract
This project was mainly concerned with two parts - testing the radio-infrared relation at low frequencies with LOFAR/MSSS data and carrying out a low-frequency case study of two nearby galaxies. It should be noted here that the efforts required to calibrate LOFAR data were considerable and are not to be underestimated. A large portion of the work throughout the project, as well as much collaboration, was required to process the data into a form which was suitable for carrying out the necessary measurements. Through collaboration with the MSSS survey access was gained to low-frequency radio measurements of a sample of nearby non-AGN galaxies which was cross-matched to infrared data from the IRAS satellite. In contrast to higher (GHz) frequencies, where the ratio of infrared to radio luminosity has long been known to be approximately constant, the relation was, for the first time, found to be flux-dependent at such low radio frequencies. The cause of this is yet unknown. The second part of this project concerned low-frequency radio observations of two nearby galaxies which were carried out with LOFAR and complemented with Westerbork observations. Spectral indices between these frequency bands were used in conjunction with Hα measurements to disentangle the thermal and non-thermal contributions to the radio flux density and thus obtain estimates of magnetic field strengths and of cosmic ray origins and transport mechanics.
Publications
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2014, Galactic and Intergalactic Magnetic Fields, Springer Praxis Books. ISBN 978-3-319-08941-6. Berlin: Springer-Verlag, 2015
Klein, U., Fletcher, A.
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2015, A&A, 582, 123
Heald, G.H., Mulcahy, D.D., Adebahr, B., Bonafede, A., Beck, R., Brüggen, M. et al.
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2017, A&A, 598, 104
Shimwell, T.W., Horneffer, A., Brüggen, M., Beck, R., Bonafede, A. et al.
