IRAS F13308+5946: A POSSIBLE TRANSITION PHASE FROM TYPE I ULTRALUMINOUS INFRARED GALAXY TO OPTICAL QUASAR

Abstract

We present a stellar population synthesis study of a type I luminous infrared galaxy: IRAS F13308+5946. It is a quasar with absolute magnitude M_i = –22.56 and has the spectral feature of a Seyfert 1.5 galaxy. Optical images show characteristics of later stages of a merger. With the help of the stellar synthesis code STARLIGHT and both Calzetti et al.'s and Leitherer et al.'s extinction curves, we estimate the past infrared (IR) luminosities of the host galaxy and find that it may have experienced an ultraluminous infrared galaxy (ULIRG) phase for nearly 300 Myr, so this galaxy has probably experienced a type I ULIRG phase. Both nuclear starburst (SB) and active galactic nuclei contribute to the present IR luminosity budget, with the SB contributing ~70%. The mass of the supermassive black hole is M _BH = 1.8 × 10⁸ M _☉ and the Eddington ratio L _bol/L _Edd is 0.12, both of which are approximate typical values of Palomar-Green QSOs. These results indicate that IRAS F13308+5946 is probably at the transitional phase from a type I ULIRG to a classical QSO.