A FIR spectroscopic survey of infrared-bright galaxies

A far-infrared (43 - 197 mu m) spectroscopic survey of a small sample of relatively nearby infrared-bright galaxies using the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) reveals a dramatic progression in emission and absorption line characteristics in these galaxies extending from strong [O III]52,88 mu m and [N III]57 mu m fine-structure line emission to detection of only faint [C II]158 mu m line emission from gas in photodissociation regions. The several ultraluminous galaxies (ULIGs) included in the full spectral sample have the weakest emission line characteristics and show absorption due to OH, H2O, CH, and [O I]. We compare the full spectra of six galaxies and examine the importance of parameters such as far-infrared extinction, density, and starburst evolution in producing the observed sequence.