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G Canalizo (IGPP/LLNL and U. Hawaii)
We test the hypothesis that QSOs are formed via strong tidal interactions or mergers, initially going through an ultraluminous infrared phase, by looking for traces to this phase in the host galaxies of QSOs. We present a systematic spectroscopic and imaging study of a sample of QSOs that may be in a transitionary stage. By modeling the spectra, we obtain ages for recent starburst events in the host galaxies and interacting companions. We find that 9 out of 9 transition QSOs are undergoing tidal interactions, and most are major mergers where at least one parent galaxy had a disk and a bulge. Every object also shows strong recent star-forming activity, and in at least 8 out of 9 cases this activity is directly related to the tidal interaction. The ages we derive for the starburst populations range from currently active star formation in some objects, to post-starburst ages \lesssim300 Myr in others. There is also a clear connection between interactions, starbursts, and QSO activity. Seven out of eight bona fide QSOs in the sample are also bona fide ULIGs. Our results imply one of two scenarios: (1) at least some ULIGs evolve to become classical QSOs, and the transition stage lasts \lesssim300 Myr, or (2) at least some QSOs are born under the same conditions as ULIGs, and their lifetime as QSOs lasts \lesssim300 Myr. We discuss other properties and trends found in the sample, and propose a model that accounts for all of them, as well as the youth of these systems.
The author(s) of this abstract have provided an email address for comments about the abstract: canalizo@igpp.ucllnl.org