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A.E. Wehrle (Interferometry Science Center, JPL/Caltech), D.L. Jones, D.L. Meier (JPL), B.G. Piner (Whittier College), S.C. Unwin (JPL)
We will use the unique capabilities of SIM to answer three key questions about active galactic nuclei and, in doing so, demonstrate in the first year of SIM operation how well the optical and radio reference frames can be linked.
1) Does the separation of the radio core and optical photocenter of the quasars used for the reference frame tie change on the timescales of their photometric variability, or is the separation stable? 2) Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? 3) Do the cores of galaxies harbor binary supermassive black holes remaining from galaxy mergers?
The first question involves tying the SIM reference frame with the International Celestial Reference Frame. We do not propose to perform the frame tie itself; instead, we will show, within about the first year, whether the frame tie will be limited by ``astrophysical noise''.
These questions address the nature of the AGN phenomenon, and the production of relativistic jets. This proposal exploits SIM's astrometric capability by measuring positions of moderately faint targets. A variety of AGN phenomena will be visible on microarcsecond scales, including position offsets between accretion disk and jet emission and position shifts due to binary black hole motion.
We acknowledge support from NASA's Origins Program.