Cowie et al. The IRAS survey showed that far-IR emission is ubiquitous among spiral and irregular galaxies, even some for which optical data suggested a very modest dust content. Some fraction of this emission is powered by young stars, making far-IR emission a very tempting indicator of star formation if we can understand it properly. For thermal emission, dust grains are heated by absorption of starlight, which operates most effectively in the blue and UV as the wavelength comes closer to the characteristic grain size. Sometimes several discrete components are fit, including very cool dust measured in the sub-mm window.
Global considerations are more interesting.
The connection may be rather indirect. The radio spectra of these systems are not the flat, thermal free-free spectra of individual H II regions, but nonthermal such as in synchrotron radiation. Apparently there is a dominant role for particles accelerated perhaps in supernova remnants, radiating while spiralling through large-scale magnetic fields. In this case, the radio emission traces star formation through the supernova rate. Radio emission is a valuable tracer in heavily obscured regions, such as IRAS-selected galaxies.