IRS spectra of faint IRAS sources

While an infrared source is always detected with the IRS at the FIRST position, only ~50% of the infrared sources are real FSC detections, as estimated from the number of sources for which the f_v_(25um) determined with the IRS is fainter than the sensitivity limit for the FSC.

Sources have 0.12<z<1.0 and luminosities 43.3<log[{nu}L_{nu}_(5.5um)]<46.7erg/s, encompassing the range from local ULIRGs to the most luminous sources discovered by Spitzer at z~2. Detectable PAH features are found in 15 of the sources (54%), and measurable silicate absorption is found in 19 sources (68%); both PAH emission and silicate absorption are present in 11 sources. PAH luminosities are used to determine the starburst fraction of bolometric luminosity, and model predictions for a dusty torus are used to determine the AGN fraction of luminosity in all sources based on vL_v_(5.5um).