The Buried QSO in IRAS F15307+3252 and the Nature of Hyperluminous Infrared Galaxies

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Abstract
We detect a highly polarized continuum and broad emission line spectrum that is typical of QSOs in the hyperluminous infrared galaxy IRAS F15307+3252. The high nonvariable polarization (p = 16%-20%) and the unpolarized narrow emission lines imply that the polarized light is produced by scattering within or near the narrow-line region. Viewed along the vantage point of the scatterers, F15307+3252 would appear to be indistinguishable from luminous optically selected QSOs. The detection of buried QSOs in the three most luminous infrared galaxies known (P09104+4109, F10214+4724, and F15307+3252) suggests that QSO activity is strongly related to the hyperluminous infrared galaxy phenomenon. Even though significant CO emission and the radio-infrared correlation suggest ongoing star formation, these objects do not distinguish themselves dramatically from other QSOs. The high frequency of companions or signs of interaction among the ultra- and hyperluminous infrared galaxies supports the idea that galaxy interaction, accompanied by star formation, is related to the energizing of an active nucleus. If these objects truly represent misdirected QSOs, then hyperluminous infrared galaxies may provide a new view of QSO host galaxies, as well as important clues to the formation and evolution of galaxies and QSOs.