Strongly gravitationally lensed quasars and the distribution of dark matter in galaxies

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AST-0607601SchechterThis project uses strongly lensed quasars (those which present multiple images due to light bending by an intervening galaxy) to study the fractional contribution of dark matter in galaxies as a function of radius, and the flattening and clumpiness of the dark matter distribution. Dark matter and conventional matter, mostly stars, make comparable contributions along the line of sight. The emitting regions of quasars are mostly small enough that individual stars act as lenses, causing fluctuations in the brightness of each image. Observations of these fluctuations will be used to measure the relative contributions, and thus the proportions, of the normal and dark matter components.Although simple models accurately reproduce the locations of multiple images, they do not correctly predict the flux ratios, presumably due to small-scale structure. Careful monitoring of these flux ratio anomalies from various quasar emission regions will be used to resolve how much is due to dark matter substructure and how much is due to micro-lensing by stars. Spectroscopic observations of the rare cases of multiple quasar images produced by spiral galaxies will be invaluable in helping to measure the relative contributions of the visible disk and dark halo to the shape of the gravitational potential.These observations will be made with the Magellan telescopes. The present principal investigator continues to work to improve image quality, which not only helps with this study but also is of value to the astronomers at all five partner institutions. Undergraduates will continue to be involved in all of this investigator's research.