Clear evidence for the early triggering of a luminous quasar-like active galactic nuclei in a major, gas-rich merger

We present deep, intermediate resolution, long-slit Gemini GMOS-S optical spectra of the Sloan Digital Sky Survey (SDSS) type II quasar J002531−104022, which is a highly disturbed system currently undergoing a major merger event. We use these data to model the ages and reddenings of the stellar populations in three distinct spatial regions and find a remarkable uniformity in the properties of the young stellar populations (YSPs) that dominate the optical spectra. The YSPs are all found to have relatively young ages (t ysp < 40 Myr), strongly implying that the latest episode of star formation and quasar activity have been triggered quasi-simultaneously. The lack of reddening deduced from both continuum modelling and the measured Balmer decrements (E(B − V) < 0.3) suggests that starburst and/or active galactic nuclei-induced outflows have already effectively removed a substantial proportion of the gas and dust from the central region. These findings starkly contrast with model predictions which suggest an offset of a few 100 Myr between the peak of merger-induced star formation and the emergence of the optically visible quasar activity. Based on our stellar population fits, we also show that the total stellar mass is in the range (4–17) × 1010 M⊙, lower than typically found for quasar host galaxies.