Dust processing in the Carina nebula region

• We analyze spectroscopic data of the ISO of the Carina nebula.
• The unidentified infrared (UIR) bands are found to be absent in the ionized gas in the Carina nebula.
• The relative intensity of the UIR band may change at the edge of the ionized region.
• A large fraction of Si in the ionized gas and silicate destruction is suggested.

Dust processing in the Carina nebula is investigated based on mid- to far-infrared spectroscopy with Infrared Space Observatory (ISO  ). Mapping observations over a central 40′×20′40′×20′ area of the nebula with PHT-S, SWS, and LWS onboard ISO not only reveal spectroscopically that the mid-infrared unidentified infrared (UIR) bands at 6.2, 7.7, 8.6, and 11.3 μm are absent in the ionized region, but also indicate that the 11.3 μm may behave differently from the other three UIR bands near the edge of the ionized region, suggesting a variation either in the size distribution or in the ionization fraction of the band carriers. The correlation of [NII]122 μm and [SiII]35 μm line emissions observed with SWS and LWS is reinvestigated based on the recent atomic data as well as the latest cosmic abundance, suggesting that a large fraction (>70>70%), if not all, of silicon returns to the gas phase in the Carina nebula, suggesting that silicates cannot survive under harsh conditions, such as massive star-forming regions. The present observations clearly show dust processing taking place in active regions in the Galaxy.