  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.
