HOST GALAXIES OF LUMINOUS TYPE 2 QUASARS AT z ∼ 0.5

We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z similar to 0.5, drawn from the Sloan Digital Sky Survey type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (M-V < -26 mag) as indicated by the [O III] lambda 5007 angstrom emission-line luminosity (L-[O (III])). Our sample has a median black hole mass of similar to 10(8.8) M-circle dot inferred assuming the local M-BH-sigma(*) relation and a median Eddington ratio of similar to 0.7, using stellar velocity dispersions sigma(*) measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad H beta, and provide an empirical calibration of the contamination as a function of L-[O (III]); the scattered-light fraction is similar to 30% of L-5100 for objects with L-[O (III]) = 10(9.5) L-circle dot. Population synthesis indicates that young poststarburst populations (< 0.1 Gyr) are prevalent in luminous type 2 quasars, in addition to a relatively old population (> 1 Gyr) which dominates the stellar mass. Broad emission complexes around He II lambda 4686 angstrom with luminosities up to 10(8.3) L-circle dot are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that similar to 5 Myr poststarburst populations contribute substantially to the luminosities (> 50% of L-5100) of all three objects with WR detections. We find two objects with double cores and four with close companions. Our results may suggest that luminous type 2 quasars trace an early stage of galaxy interaction, perhaps responsible for both the quasar and the starburst activity.