Discovery and analysis of dust -reddened type 1 quasars - Finding the missing link in quasar evolution
One of the most important discoveries in recent times has been that the properties of the galaxies are proportional with the mass of the super-massive black hole in the center of the galaxy, which suggests that their growth was at some point linked.
In this thesis, I explore the population of dust-reddened broad lined quasars. These so-called red quasars might be the missing link in quasar evolution between quasars and starburst galaxies. As the two galaxies are merging, large columns of gas and dust from the hosts enshroud the quasar and provide feeding material for the starbursts. This would be an evolutionary step before becoming a blue quasar/elliptical galaxy system.
I describe how going after very red objects with radio counterparts, we are finding dust-reddened broad lined quasars with more than 50% success. At high redshifts, there is an unusually high fraction of Low Ionization Broad Absorption Line Quasars (LoBALs), a population which has often been invoked as being an early phase in the lifetime of a quasar. X-ray imaging and spectroscopy of a subsample of these red quasars have shown that they are all obscured, but not to the degree typically associated with torus obscuration. X-ray spectral indices also indicate high accretion efficiencies, a phenomenon associated with young quasars.
HST imaging of 13 of these dust-reddened quasars have found a large fraction (85%) of objects associated with major mergers showing tidal tails and double nuclei. None of the light profiles of the host galaxy fit an elliptical profile. This high interaction fraction is significantly higher than the typical 30% seen in host galaxies of blue quasars.
Furthermore, Spitzer observations show mid-infrared spectra that resemble the ones of Ultraluminous Infrared Galaxies (ULIRGs) for the quasars which show most interaction. ULIRGs are usually associated with extreme bursts of star formation. In the end, all of these clues confirm the thesis that red quasars are a young phase in the lifetime of a quasar.