A polarimetric search for hidden quasars in three radio-selected ultraluminous infrared galaxies

We have carried out a spectropolarimetric search far hidden broad-line quas ars in three ultraluminous infrared galaxies (ULIRGs) discovered in the pos itional correlations between sources detected in deep radio surveys and the IRAS Faint Source Catalog. Only the high-ionization Seyfert 2 galaxy TF J1 736 + 1122 is highly polarized, displaying a broad-line spectrum visible in polarized light. The other two objects, TF J1020 + 6436 and FF J1614 + 323 4, display spectra dominated by a population of young (A type) stars simila r to those of "E + A" galaxies. They are unpolarized, showing no sign of hi dden broad-line regions. The presence of young starburst components in all three galaxies indicates that the ULIRG phenomenon encompasses both active galactic nuclei (AGNs) and starburst activity, but the most energetic ULIRG s do not necessarily harbor "buried quasars." We find that a luminous infra red galaxy is most likely to host an obscured quasar if it exhibits a high- ionization ([O III] lambda 5007/H beta greater than or similar to 5) spectr um typical of a "classic" Seyfert 2 galaxy with little or no Balmer absorpt ion lines, is "ultraluminous" (L-IR greater than or similar to 10(12) L-.), and has a "warm" IR color (f(25)/f(60) greater than or similar to 0.25). T he detection of hidden quasars in this group but not in the low-ionization, starburst-dominated ULIRGs (classified as LINERs or H II galaxies) may ind icate an evolutionary connection, with the latter being found in younger sy stems.