Mathematics – Logic
Scientific paper
Jul 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001hst..prop.9212r&link_type=abstract
HST Proposal ID #9212
Mathematics
Logic
Hst Proposal Id #9212 Cosmology
Scientific paper
Weak gravitational lensing has become an important probe of the geometry and large-scale structure of the universe. Galaxy-galaxy lensing is a well established result, and the focus has now shifted to the measurement of `cosmic shear', i.e. the weak gravitational lensing of galaxy images caused by the large scale distribution of dark matter. A number of ground based programs have announced the presence of this shear and using the HST Medium Deep Survey database we have tentatively detected such a shear at smaller angular scales, corresponding to larger cosmological distances. Confirmation and reduction of errors in the detection of this elusive effect has however, been complicated by various systematics in the observational data which can masquerade the true signal. The MDS database was optimized for galaxy morphology ignoring several second order effects which could not be addressed a few years ago. Recent reconstruction by ST-ECF of the jitter files for all HST WFPC2 observations, and the detailed models for the HST focus position has set the stage for a more rigorous reanalysis as required for a more confident measurement of cosmic shear. Well characterized WFPC2 observations from the rigorously monitored HST provide the best hope for the robust measurement of cosmic shear in the near future and will set the stage for more precise measurements with the Advanced Camera.
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