Young stellar populations in type II quasars: timing the onset of star
  formation and nuclear activity
  Despite the emerging morphological evidence that luminous quasar-like AGN are
triggered in galaxy mergers, the natures of the triggering mergers and the
order of events in the triggering sequence remain uncertain. In this work, we
present a detailed study of the stellar populations of the host galaxies of 21
type II quasars, with the aim of understanding the sequence of events between
the onset of the merger, the triggering of the associated starburst and the
initiation of the quasar activity. To this end, we model high quality, wide
spectral coverage, intermediate resolution optical spectra of the type II
quasars. We find that of the 21 objects, the higher-order Balmer absorption
lines, characteristic of young stellar populations (YSP) , are directly
detected in ~62% of the sample. We also fit these spectra using a number of
combinations of stellar and/or power-law components, representative of viable
formation histories, as well as including the possibility of scattered AGN
light. We find that 90 % of the type II quasar host galaxies require the
inclusion of a YSP to adequately model their spectra, whilst 71 % of the sample
require the inclusion of a YSP with age < 100 Myr. Since the ages of the YSP in
most type II quasar host galaxies are comparable with the expected lifetimes of
the AGN activity, these results provide strong evidence that the quasars are
triggered close to the peaks of the merger-induced starbursts.
