2009ApJ...702.1098L

We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z ∼ 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] λ5007 Å emission-line luminosity (L_[O III]_). Our sample has a median black hole mass of ∼10^8.8 M_☉ inferred assuming the local M_BH-σ_* relation and a median Eddington ratio of ∼0.7, using stellar velocity dispersions σ_* measured from the G band. We estimate the contamination of the stellar continuum from scattered quasar light based on the strength of broad Hβ, and provide an empirical calibration of the contamination as a function of L_[O III]_; the scattered-light fraction is ∼30% of L₅₁₀₀ for objects with L_[O III]_= 10^9.5 L_☉. 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 λ4686 Å with luminosities up to 10^8.3 L_☉ are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet (WR) populations. Population synthesis shows that ∼5 Myr poststarburst populations contribute substantially to the luminosities (>50% of L₅₁₀₀) 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.