Speaker
Description
Radio continuum emission has the potential to be an extinction-free star formation tracer in galaxies near and far. Low-frequency radio continuum observations can give us new insights into the workings as well as the limitations of the radio-star formation rate (radio-SFR) relation. We used maps from a sample of nearby galaxies including both low- and high-band data from the LOw Frequency ARray and ancillary data in the radio continuum and infrared. Studying the radio-SFR relation at low frequencies we find deviations from the simple power-law spectrum that we would expect for a calorimetric cosmic-ray electron spectrum. In particular we find a super-linear radio-SFR relation, where the more massive galaxies are better electron calorimeters than their lighter counterparts. This can be judged on the basis of the radio spectral index where less massive galaxies have flat spectra in contrast to more massive galaxies that have steep spectra. We were able to calibrate the influence of the radio spectral index with spatially resolved observations and show that the global and local radio-SFR relation can be unified. Then, with ultra-low frequency observations we explored absorption processes in star-forming regions. We demonstrated that both ionisation losses of cosmic-ray electrons in the neutral medium and free-free absorption of radio continuum radiation in the ionised medium play a role in the shaping the radio continuum spectrum. This may potentially limit the use of radio continuum as a star-formation tracer below 100 megahertz.
