Speaker
Description
Co-evolution with active galactic nuclei (AGN) is extensively invoked to explain the properties of massive galaxies and the growth of supermassive black holes. Stellar populations and recent star-formation histories (SFHs), which can help constrain the processes involved in this co-evolution, are challenging to obtain for quasar host galaxies without special decomposition techniques. We use Mean-Field Independent Component Analysis (MFICA) to decompose quasar spectra and determine the stellar populations and SFHs of their host galaxies.
We apply MFICA decomposition to SDSS DR7 quasars (0.16 < z < 0.8), finding that quasars are hosted predominantly (~44% of our quasars) by star-forming galaxies and have, on average, younger stellar populations than a control sample of mass-matched galaxies. We also find that nearly 24% of our quasars are hosted by post-starburst galaxies – a significant excess (~10-20 times) compared to the fraction of post-starburst galaxies in the overall galaxy population. The heterogeneity of quasar hosts points to multiple feeding mechanisms, whilst the excess of massive post-starburst hosts points to the conduciveness of the post-starburst phase for quasar activity, possibly due to major mergers. Additionally, we compare our results to the host galaxies of Type-2 Quasars/AGNs, investigating if their hosts are identical (as per the unified model), or if they are distinct and follow a merger/obscuration-based evolutionary picture.
