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Session 67 - ISM in Galaxies.
Display session, Wednesday, January 15
We are using the Infrared Space Observatory (ISO) to observe a variety of ISM diagnostics in about 70 star forming galaxies. The goal is to derive the physical properties of the interstellar gas, dust and radiation field in a broad sample of normal disk galaxies, and to study the star formation process on a global scale, looking for drivers and inhibitors. We use LWS to measure ionic and atomic fine-structure lines ([CII], [OI], [NII] 122\mum, [NIII] 57\mum, [OIII] 88\mum amp; 52\mum) and the continuum between 50 and 180\mum. We use CAM to image these galaxies at 7 and 15\mum with 7^\prime\prime effective resolution, and PHT-S to obtain spectro-photometry in the 3 to 12\mum range. The sample includes about sixty distant galaxies where global properties are measured, and about ten nearby galaxies, within which selected regions are studied to characterize differences between arms, diffuse disk and nuclear regions.
We show examples of the fine-structure line data from a few galaxies, and discuss the large variations in relative line strengths among them; extreme examples of line deficiency are discussed in a companion paper by Malhotra et al. (this meeting). Considerably improved calibration is needed before the line fluxes can be compared to theoretical models of PDRs or HII regions, but the data already suggest empirical correlations between relative line strengths and galaxy properties. The CAM mid-infrared images allow us to gauge the intensity of the heating radiation as discussed in the companion paper by Silbermann et al. (this meeting). The mid-infrared spectroscopy complements the imaging and demonstrates the dominance of PAH features in all objects so far observed (Lu et al. this meeting).
ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom), and with the participation of ISAS and NASA.
Program listing for Wednesday