Dust processing in the Carina nebula region

摘要

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' x 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 mu m are absent in the ionized region, but also indicate that the 11.3 mu m 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 mu m and [SiII]35 mu m 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%), 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. (C) 2015 Elsevier Ltd. All rights reserved.