  It was once common to regard Seyfert and starburst galaxies as completely
different types of object, but there is growing recognition that these
classifications refer to the extremes of a continuous spectrum of galaxy types.
In a previous study we investigated a sample of galaxies with ambiguous optical
emission-line ratios and concluded from near-infrared spectroscopic
observations that the sample consisted of composite galaxies, containing both a
starburst and an active galactic nucleus (AGN). We now extend our study using
radio synthesis and long-baseline interferometer observations made with the
Australia Telescope, together with far-infrared IRAS observations, to discuss
the relative contribution of starburst and AGN components to the overall
luminosity of the composite galaxies. We find that only a small fraction of the
radio emission (<10%) can be attributed to an AGN, and that the majority of the
far-infrared emission (>90%) is probably due to the starburst component. We
also show that an AGN contribution to the optical emission of as little as 10%
is sufficient to account for the ambiguous line-ratio diagnostics.
