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Session 98 - AGN-Absorption/Emission.
Display session, Thursday, January 16
Metropolitan Ballroom,
New mid-infrared (10 and 20 \mum) spectroscopy of the ultraluminous infrared galaxy IRAS 08572+3915 is presented. The 10 \mum spectrum reveals a deep silicate absorption feature, while the 20 \mum spectrum shows no clear evidence for an 18 \mum silicate absorption feature. An interstellar extinction curve is fitted to IRAS 08572+3915 and two other deep silicate infrared galaxies, NGC 4418 and Arp 220. It is found that pure extinction cannot explain the spectral energy distributions of these sources. On the other hand, both the strength of the silicate absorption and the overall spectral energy distributions of the three galaxies agree well with scaled-up models of galactic protostars. From this agreement, we conclude that the infrared emission comes from an optically thick dust shell surrounding a compact power source. The size of the power source is constrained to be smaller than a few parsecs. We argue that accretion onto a supermassive black hole, rather than a burst of star formation, is more likely to be the power source.
