The active nucleus in the ultraluminous infrared galaxy IRAS 08311-2495

Near-infrared spectroscopy using the new Palomar Integral Field Spectrograp h indicates the presence of an active galactic nucleus (AGN) in the ultralu minous infrared galaxy IRAS 08311-2459. The high-velocity wings of the Pasc hen-alpha hydrogen recombination line are seen to be spatially unresolved, with no positional offset between red and blue high-velocity emission. The [Si VI] coronal line, with a 167 eV excitation potential, is also spatially unresolved, with a velocity width comparable to that of the broad componen t of the Paa emission. The low-velocity component of the Paa emission is se en to be rotating and is extended over similar to 2 kpc. Molecular hydrogen is also extended, and it is elongated along the maximum velocity gradient, sharing the same rotation profile as the narrow Pact emission. The simple picture in agreement with the observations is that of an AGN surrounded by a rotating disk of star formation. These observations lend strength to the usage of [Si VI] as a diagnostic of AGN activity in ultraluminous infrared galaxies and also highlight the utility of integral held spectroscopy in el ucidating subtle morphological differences in line-emitting regions.