New 325 MHz observations of H II galaxies - The mechanisms that shape the unusual radio spectra

The B array of the VLA has observed a sample of seven H II galaxies at 325 and 1489 MHz; the radio continuum spectra thus obtained exhibit a wide variety of spectral shapes, but four show a significant flattening toward lower frequencies. A detailed discussion is conducted of this LF flattening, invoking several radio emission and absorption mechanisms and energy losses of relativistic electrons. Such model-dependent parameters as the spectral index of injected electrons, the radio-emission spectral index, the thermal electron density, and the age of the relativistic electrons, are derived.