Follow-up near-infrared spectroscopy of ultraluminous infrared galaxies observed by ISO

We present low resolution near-infrared spectroscopy of an unbiased sample of 24 ultraluminous infrared galaxies (ULIRGs), selected from samples previously observed spectroscopically in the mid-infrared with the Infrared Space Observatory (ISO). Qualitatively, the near-infrared spectra resemble those of starbursts. Only in one ULIRG, IRAS 04114-5117E, do we find spectroscopic evidence for AGN activity. The spectroscopic classification in the near-infrared is in very good agreement with the mid-infrared one. For a subset of our sample for which extinction corrections can be derived from Pa alpha and Br gamma, we find rather high Pa alpha luminosities, in accordance with the powering source of these galaxies being star formation. [FeII] emission is strong in ULIRGs and may be linked to starburst and superwind activity. Additionally, our sample includes two unusual objects. The first, IRAS F00183-7111, exhibits extreme [FeII] emission and the second, IRAS F23578-5307, is according to our knowledge one of the most luminous infrared galaxies in H-2 rotation-vibration emission.