DEEP INFRARED GALAXIES

We present high signal-to-noise ratio optical spectra of 17 infrared-bright emission-line galaxies near the north ecliptic pole. Reddening-corrected line ratios [O III] lambda-5007/H-beta, [N II] lambda-6583/H-alpha, [S II] (lambda-6716 + lambda-6731)/H-alpha, and [O I] lambda-6300/H-alpha are used to discriminate between candidate energy generation mechanisms in each galaxy. These criteria have frequently been applied to optically selected samples of galaxies in the past, but this is the first time they have been applied to a set of faint flux-limited infrared-selected objects. The analysis indicates the sample contains seven starburst galaxies and three active galactic nuclei (AGNs). However, seven galaxies in our sample elude the classification scheme based on these line ratios. We conclude that a two-component (starburst plus AGN) model for energy generation in galaxies is inadequate for infrared galaxies.