Host Galaxies of Luminous Type

We present deep Gemini GMOS optical spectroscopy of nine luminous quasars at redshifts z ∼ 0.5, drawn from the SDSS type 2 quasar sample. Our targets were selected to have high intrinsic luminosities (MV < −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 ∼ 10M⊙ inferred assuming the local MBH-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 L⊙. Population synthesis indicates that young post-starburst 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 10L⊙ are unambiguously detected in three out of the nine targets, indicative of Wolf-Rayet populations. Population synthesis shows that ∼5-Myr post-starburst populations contribute substantially to the luminosities (> 50% of L5100) of all three objects with Wolf-Rayet 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. Subject headings: galaxies: active — galaxies: evolution — galaxies: interactions — galaxies: nuclei — galaxies: starburst — galaxies: stellar content — quasars: general