The Active Nucleus in the Ultraluminous Infrared Galaxy IRAS 08311-2459
  Near-infrared spectroscopy using the new Palomar Integral Field Spectrograph indicates the presence of an AGN (active galactic nucleus) in the ultraluminous infrared galaxy IRAS 08311-2459. The high-velocity wings of the Paschen-alpha hydrogen recombination line are seen to be spatially unresolved, and 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 component of the Pa-alpha emission. The low velocity component of the Pa-alpha emission is seen to be rotating, and is extended over about 2 kpc. Molecular hydrogen is also extended, and elongated along the maximum velocity gradient, sharing the same rotation profile as the narrow Pa-alpha 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 field spectroscopy in elucidating subtle morphological differences in line emitting regions. 
T. W. Murphy Jr., B. T. Soifer, K. Matthews, L. Armus