Detection of Systematic Gravitational Lens Galaxy Image Alignments: Mapping Dark Matter in Galaxy Clusters.

Systematic gravitational lens alignment of 10-60 faint background galaxy images has been detected, centered on foreground galaxy clusters of high velocity dispersion. The background galaxy population is selected by its extreme blue B-R color. At a limiting surface brightness of 29 B magnitude arcsec sup (-2) there are 30 background galaxies arcmin sup (-2) mag sup (-1) anywhere in the sky, which is sufficient to statistically map the dark matter distribution in a foreground cluster. Automated pattern recognition software generates a 2-d lens distortion map. Initial results for the high velocity dispersion clusters A1689 and CL1409+52 are presented here. The dark matter is apparently correlated (center and radial extent) with the cluster red light, suggestive of a baryonic origin or dissipative coupling. The existence of a high percentage of lens-distorted faint blue galaxies sets a lower limit of approximately 0.9 to this background galaxy population mean redshift.