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M. Imanishi (Nat'l Astronomical Obs., Japan)
We report on 3--4 \mum slit spectroscopy of 13 Seyfert 2 nuclei. The 3.3 \mum polycyclic aromatic hydrocarbon (PAH) emission is used to estimate the magnitudes of compact nuclear starbursts (on scales less than a few 100 pc) and to settle the controversy over their energetic importance in Seyfert 2 nuclei, making use of two important advantages of this emission as a diagnostic of starburst activity: (1) the uncertainty in the correction for dust extinction is small compared with shorter wavelengths, and (2) even weak starbursts are detectable. For three selected Seyfert 2 nuclei that have been well studied in the UV, the magnitudes of the compact nuclear starbursts estimated from the 3.3 \mum PAH emission (with no extinction correction) is in satisfactory quantitative agreement with that based on the UV after extinction correction. This agreement indicates that the flux attenuation of compact nuclear starburst emission due to dust extinction is insignificant at 3--4 \mum, and thus allows us to use the observed 3.3 \mum PAH luminosity to estimate the magnitudes of the compact nuclear starbursts in Seyfert 2 nuclei. Based on our 3--4 \mum slit spectra, the following main conclusions are drawn: (1) except in one case, the observed nuclear 3--4 \mum emission is dominated by AGN and not by starbursts, (2) compact nuclear starbursts are detected in 8 out of 13 Seyfert 2 nuclei, but cannot dominate the energetics of the galactic infrared dust emission in the majority of the observed Seyfert 2 galaxies, and (3) more powerful AGNs tend to be related to more powerful compact nuclear starbursts, provided that the 12 \mum luminosity measured with IRAS is a good measure of AGN power. MI is funded by NAOJ.