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E. Sturm (MPE)
The Space InfraRed Telescope Facility (SIRTF) will mark the advent of a new era in the exploration of our Universe in the infrared. The order-of-magnitude improvements in capability of SIRTF over existing programs will catapult to new levels our ability to probe the distant Universe. Deep infrared observations will be crucial for answering fundamental questions regarding the formation and early evolution of galaxies, the source of the extragalactic background at low and high energies, and the origin of nuclear activity in galaxies. Quantitative mid-infrared low- and high-resolution spectroscopy with SIRTF will be required for source identifications and redshift determinations, and will be decisive in determining the detailed properties of these sources, including the relative roles of star formation and AGNs in providing their bolometric luminosity.
With the Infrared Space Observatory (ISO) much progress has been made in our understanding of mid-infrared spectra. Quantitative methods have been devised to identify the nature of the energy source in infrared bright galaxies, and to characterize the properties of obscured starbursts (e.g, age, IMF) and AGNs (e.g., ionizing spectrum, cloud distribution). These methods are based on the flux ratios of forbidden and recombination emission lines, as well as on dust emission features and continuum shapes. We summarize the various diagnostic tools and their current status, including most recent modeling work. We also emphasize the unsolved problems and the steps that must be taken to exploit SIRTF's full potential.