Mathematics – Logic
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8631g&link_type=abstract
HST Proposal ID #8631
Mathematics
Logic
Hst Proposal Id #8631 Agn/Quasars
Scientific paper
enlargethispage0.25in We propose to expand our Cycle 8 second generation HST snapshot survey of bright quasars, optimized to find lenses with component image separations < 1". Most models of quasar lensing predict distributions which peak at separations in the range 0arcs5 to 1", yet the observed distribution of lenses peaks at 1arcs3. The lack of systems with close separations is difficult to reconcile with a flat universe, preferred by theory {inflation} and the observational determinations of the cosmological constant from type Ia supernovae. Our Cycle 8 survey improves over the earlier pre-refurbishment snapshot survey of quasars {Bahcall et al. 1992; Maoz et al. 1993} in several important respects. With the restored PSF and the image quality of STIS, the new images are considerably more sensitive to the presence of both close separation and faint lens components. Our snapshots are guided, multiple exposure observations, allowing a much better final data product. We are also obtaining exposures in both Clear and LongPass modes, providing immediate color information to gauge the chances that a pair of close images is consistent with lensing. At the time of this writing, about 80 of our 300 allocated snapshots have been taken. The early returns are exciting: we have one small {0arcs6} separation lens, plus 3 additional lens candidates at larger separations. Encouraged by these results, we propose to expand the survey in Cycle 9.
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