Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812002h&link_type=abstract
American Astronomical Society, AAS Meeting #218, #120.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Statistical weak gravitational lensing of background galaxy images by foreground galaxies is now a widely used and powerful tool to probe the distribution of galactic dark matter. However, such analysis often depends on an assumption of a single, weak deflection of the background rays by a foreground lensing object.
I will present results that demonstrate the importance of considering multiple deflections when interpreting weak shear results. In particular, I show that multiple deflections can introduce systematic depression of γ+ - the anisotropic shear with respect to the major axis of the lens, and a corresponding amplification of γ-. Such systematics can lead to reduced estimates of the degree of flattening of galaxy dark matter halos, or even the conclusion that dark matter halos are anti-aligned with the light.
I create two complimentary simulation spaces to explore these effects. One is a simple system consisting of a single lens whose dark matter halo shape and orientation are known. The subject lens is then embedded in an environment of masses distributed in redshift space. Apparent shear of background sources is found in the usual way and results are tabulated both using apparent lens shape and PA (as an observer would) and using actual shape and PA.
A second simulation space replicates as nearly as possible a real observational dataset. I use this simulation to help overcome the systematic effects introduced by multiple deflections to infer actual halo shapes. From this result, I make a modest (95%) detection of flattened dark matter halos aligned with the light and that an NFW type density profile is preferred (95%) over an isothermal density profile. Detection of an isotropic lensing signal as demanded by MOND is similarly excluded.
Support from the National Science Foundation under contract AST-0708468 is gratefully acknowledged.
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