Discovery of a Galaxy Cluster via Weak Lensing
We report the discovery of a cluster of galaxies via its weak gravitational lensing effect on background galaxies, the first spectroscopically confirmed cluster to be discovered through its gravitational effects rather than by its electromagnetic radiation. This fundamentally different selection mechanism promises to yield mass-selected, rather than baryon- or photon-selected, samples of these important cosmological probes. We have confirmed this cluster with spectroscopic redshifts of 15 members at z = 0.276, with a velocity dispersion of 615 km s^(-1). We use the tangential shear as a function of source photometric redshift to estimate the lens redshift independently and find z_l = 0.30 ± 0.08. The good agreement with the spectroscopy indicates that the redshift evolution of the mass function may be measurable from the imaging data alone in shear-selected surveys.
Additional Information© 2001. The American Astronomical Society. Received 2001 April 5; accepted 2001 July 10; published 2001 July 23. We thank P. Guhathakurta for providing spectroscopic redshifts outside the cluster and the CTIO staff for their help with the BTC project and for their upgrading and maintenance of the delivered image quality of the Blanco telescope. The CTIO is a division of National Optical Astronomy Observatory (NOAO), which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation (NSF). BTC construction was partially funded by the NSF.
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