Dartmouth Events

Abstract: Supermassive black hole binaries seem to be an inevitable product of the prevailing galaxy evolution scenarios where most massive galaxies play host to a central black hole and undergo a history of mergers and accretion over the course of cosmic time. The early stages of this process have been observed in the form of interacting galaxy pairs as well as kiloparsec separation dual active galactic nuclei, but the close, bound binaries that are expected to follow have proven elusive. The detection of this population would contribute important evidence in favor of heirarchical galaxy evolution scenarios, and is also of interest in other fields including gravitational wave astronomy. With this motivation, I have undertaken a systematic search for close supermassive black hole binaries based on the hypothesis that the secondary black hole in the system is active and the resulting broad emission lines will be doppler shifted due to its orbital motion (analogous to a single-line spectroscopic binary). The sample of 88 binary candidates is therefore selected from z<0.7 SDSS quasars via substantial (>1000 km/s) shifts of their broad H-beta lines relative to their systemic redshifts. I will present an update on my efforts to evaluate the credentials of these candidates via their multi-year spectroscopic variability properties and radial velocity curves.