3.28 mu-m feature and continuum emission in galaxy nuclei.

Low resolution spectra around 3.3 μm have been obtained for 28 galaxy nuclei whose optical emission line spectra range from H II region like to pure Seyfert type 1. The 3.28 μm emission feature has been detected (≥3σ) in 70% of the H II region, 65% of the mixed H II/Seyfert, 18% of the Seyfert 2 and none of the Seyfert 1 nuclei. It appears that the 3.28 μm feature is a useful discriminator between star formation and Seyfert activity in galaxy nuclei. Broadband infrared photometry together with measurements of the Br γ hydrogen recombination line have been used to estimate separately the stellar, free-free and thermal dust emission components of the 3.3 μm continuum in those nuclei exhibiting the 3.28 μm emission feature. Intermediate band photometry around 10 μm reveals structure attributable to the (7.7 μm), 8.6 μm and 11.25 μm features in those cases where the 3.28 μm feature is clearly present.