Abstract
Radio sources with larger negative indices (α < -0.1, where the spectral index α is defined by Sν ≡ να) have been found in regions of star formation. In this paper, the authors explore whether these spectral indices could be obtained from sources of free-free emission with ad hoc electron density and temperature distributions. They find that, if only free-free emission and absorption are involved, the spectral index will always be α ≥ -0.1 regardless of the source characteristics. Finally, the authors explore the possibility that the large negative spectral indices could be produced by dust absorption. However, the very high column densities required lead them to conclude that the large negative indices found in these peculiar sources are more naturally explained in terms of optically thin synchrotron emission.
