The blueshifted Paα broad line component and the origin of strong iron emission in the ultraluminous infrared galaxy IRAS 07598+6508

We present the Paα emission profile of the ultraluminous infrared galaxy (ULFIRG) IRAS 07598+6508 which is an unusually strong Fe II emitter in the optical. The Paα emission line profile shows a blueshifted broad component (FWHM ≃3900 km s^-1) together with a narrow core (FWHM≤530 km s^-1). The presence of the broad line component strongly suggests that IRAS 07598+6508 has an active galactic nucleus, supporting a scenario of merger-induced quasar formation proposed by Sanders et al. [ApJ, 325, 74 (1988)], although we cannot rule out the possibility of a supernova-driven high speed wind. Possible detection of [Fe II]1.893 μm emission is also reported. It is shown that strong Fe II emitters such as IRAS 07598+6508 have intermediate IRAS color properties between normal quasars and cold ultraluminous infrared galaxies. We thus suggest an evolutionary link from cold ULFIRG through warm ULFIRG and Fe II ULFIRG to quasars.