Ultra-High Resolution Studies of AGNs III: nuclear extent and the SIM astrometric grid

Details Ultra-High Resolution Studies of AGNs III: nuclear extent and the SIM astrometric grid Ultra-High Resolution Studies of AGNs III: nuclear extent and the SIM astrometric grid

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8727s&link_type=abstract

HST Proposal ID #8727

Computer Science

Performance

Hst Proposal Id #8727 Agn/Quasars

Scientific paper

We successfully completed a pilot project using the original Fine Guidance Sensor astrometer {FGS3} to study optical extent of several AGN. We will extend this work using the significantly enhanced performance of the new FGS1R. We will re-observe two high S-N AGN from our earlier sample, probing the broad line region at 10mas resolution. In an important extension of the work, we will observe two classes of nearby AGN deemed suitable for the Space Interferometry Mission {SIM} extragalactic grid. Stable, point-like extragalactic sources are needed to provide a frame tie from the SIM galactic grid to a global astrometric reference frame {e.g. ICRF}. Because of their relative brightness, nearby BL Lac & Seyfert 1 objects make up a large fraction of the flux- limited sample of grid objects. Based on our pilot and the improved FGS1R performance, we will probe angular sizes of 5- 10 mas for these sources. Resolved structure at these scales would have profound implications for AGN models. Conversely, if the nuclear emission remains point-like at the finer resolution possible with FGS1R, then more stringent limits to the size of the broad line region and and surrounding emission can be established. Our program thus has a unique complementarity: resolved structure will be of general scientific interest, while upper limits to structure will help produce a reliable input catalog for the SIM astrometric grid.

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