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H.D. Tran, M.S. Brotherton, S.A. Stanford, W. van Breugel (IGPP/LLNL), A. Dey (NOAO), D. Stern (UC Berkeley), R. Antonucci (UC Santa Barbara)
Using the Keck 10-m telescope, we have carried out a spectropolarimetric search for hidden broad-line quasars in three ultraluminous infrared galaxies (ULIRGs) discovered in the positional correlations between sources detected in deep radio surveys and the IRAS Faint Source Catalog. Only the high-ionization Seyfert 2 galaxy TF J1736+1122 is highly polarized, displaying a broad-line spectrum visible in polarized light. The other two objects, TF J1020+6436 and FF J1614+3234, display spectra dominated by a population of young (A-type) stars similar to those of ``E + A'' galaxies. These galaxies are unpolarized, showing no sign of hidden broad-line regions. The presence of young starburst components in all three galaxies indicates that the ULIRG phenomenon encompasses both AGN and starburst activity, but the most energetic ULIRGs do not necessarily harbor ``buried quasars''. By comparing these results with previous studies of obscured quasars in ULIRGs, we found that both the ionization level and infrared color are important in determining whether an ULIRG contains a genuine buried quasar.