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The most luminous infrared galaxies (IRGs) found in the IRAS all sky survey have now been shown to have luminosities nearly as great as the most luminous QSOs. The most distant such system currently known, FSC10214+4724, is at a redshift of 2.29. These Hyperluminous IRGs (HIRGs) have very large amounts of hot dust emission in the 3 to 100 um range, enabling the moderate mission SIRTF to discover and study in detail large samples of these systems out to redshifts of 10, if they exist in substantial numbers at such early epochs.
Confusion limited deep imaging with SIRTF could detect systems such as 10214 at wavelengths of 60um and greater to redshifts as great as 10, while infrared spectroscopy of dust features and/or hydrogen lines could establish their distances to well beyond a redshift of 5. Less extreme examples of Infrared Luminous galaxies, such as Arp 220, could be detected to redshifts greater than 2. Coordinated deep imaging surveys and spectroscopic followup can establish the cosmic evolution of these systems to the highest redshifts where they are found.
There are a large number of infrared fine structure lines (Voit,M., Ap.J. 399, 495) that can be used to probe the ionization conditions, electron density and extinction in the highly obscured nuclear regions of High Luminosity Infrared galaxies in via moderate resolution infrared spectroscopy. Such studies with SIRTF spectrometers will distinguish between starburst and AGN ionization mechanisms. They will also diagnose the physical conditions in the emitting regions. These data are necessary for an understanding of the emission process.
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