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L.V.E. Koopmans (Caltech), R.D. Blandford (Caltech), A.G. de Bruyn (NFRA), C.D. Fassnacht (STScI), J. Wambsganss (Potsdam University)
Galactic microlensing results from the MACHO, EROS and OGLE collaborations suggest that a significant fraction (~20%) of the dark-matter halo inside 50~kpc might be composed of massive compact objects with typical masses of ~0.6~M\odot. Direct searches for high proper-motion objects in the solar neighborhood and HDF suggest that these objects could be white dwarfs, although a high mass fraction posses substantial problems for standard star-formation models.
We present new VLA multi-frequency radio observations of the edge-on spiral gravitational lens B1600+434 at a redshift z=0.41. They show strong non-intrinsic variations in the lensed image that passes predominantly through the dark-matter halo around the lens galaxy. We argue that these variations are the result of microlensing.
The halo line-of-sight in Galactic microlensing observations and that in B1600+434 are similar, allowing for a unique comparison of these fully independent results from two spiral galaxies. We present results of this comparison and discuss whether the microlensing populations in B1600+434 and our Galaxy, and the population of high proper-motion objects can be the same.
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The author(s) of this abstract have provided an email address for comments about the abstract: leon@tapir.caltech.edu