THE PROPERTIES OF POST-STARBURST QUASARS BASED ON OPTICAL SPECTROSCOPY

Abstract

We present optical spectroscopy of a sample of 38 post-starburst quasars\n(PSQs) at z ~ 0.3, 29 of which have morphological classifications based on\nHubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs)\npossess the spectral signatures of massive intermediate-aged stellar\npopulations making them potentially useful for studying connections between\nnuclear activity and host galaxy evolution. We model the spectra in order to\ndetermine the ages and masses of the host stellar populations, and the black\nhole masses and Eddington fractions of the AGNs. Our model components include\nan instantaneous starburst, a power-law, and emission lines. We find the PSQs\nhave MBH ~ 10^8 Msun accreting at a few percent of Eddington luminosity and\nhost ~ 10^10.5 Msun stellar populations which are several hundred Myr to a few\nGyr old. We investigate relationships among these derived properties, spectral\nproperties, and morphologies. We find that PSQs hosted in spiral galaxies have\nsignificantly weaker AGN luminosities, older starburst ages, and narrow\nemission-line ratios diagnostic of ongoing star-formation when compared to\ntheir early-type counterparts. We conclude that the early-type PSQs are likely\nthe result of major mergers and were likely luminous infrared galaxies in the\npast, while spiral PSQs with more complex star-formation histories are\ntriggered by less dramatic events (e.g., harassment, bars). We provide\ndiagnostics to distinguish the early-type and spiral hosts when high spatial\nresolution imaging is not available.\n