The Properties of Post-Starburst Quasars Based on Optical Spectroscopy
  We present optical spectroscopy of a sample of 38 post-starburst quasars
(PSQs) at z ~ 0.3, 29 of which have morphological classifications based on
Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs)
possess the spectral signatures of massive intermediate-aged stellar
populations making them potentially useful for studying connections between
nuclear activity and host galaxy evolution. We model the spectra in order to
determine the ages and masses of the host stellar populations, and the black
hole masses and Eddington fractions of the AGNs. Our model components include
an instantaneous starburst, a power-law, and emission lines. We find the PSQs
have MBH ~ 10^8 Msun accreting at a few percent of Eddington luminosity and
host ~ 10^10.5 Msun stellar populations which are several hundred Myr to a few
Gyr old. We investigate relationships among these derived properties, spectral
properties, and morphologies. We find that PSQs hosted in spiral galaxies have
significantly weaker AGN luminosities, older starburst ages, and narrow
emission-line ratios diagnostic of ongoing star-formation when compared to
their early-type counterparts. We conclude that the early-type PSQs are likely
the result of major mergers and were likely luminous infrared galaxies in the
past, while spiral PSQs with more complex star-formation histories are
triggered by less dramatic events (e.g., harassment, bars). We provide
diagnostics to distinguish the early-type and spiral hosts when high spatial
resolution imaging is not available.
