AAS Meeting #193 - Austin, Texas, January 1999
Session 108. Gravitational Lensing
Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1

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[108.10] Observational Cosmology with a Small Telescope: A Search for Amplification Bias

D. J. Norman (U. Washington), C. D. Impey (U. Arizona)

Weak gravitational lensing by clusters and superclusters can change our perception of the distribution of bright background quasars through a phenomenon known as amplification bias. It has been suggested that this lensing will lead to an association of moderate redshift quasars (z ~1.0-2.0) and forground galaxies (z ~0.2-0.3 ).

Earlier studies have had mixed results detecting an angular correlation signal between background quasars and foreground galaxies. These inconsistences are possibly the result of differing slopes of the quasar source function for the samples chosen, and are likely not due to dust in the foreground clusters. Most of the previous studies of this correlation have used existing photographic surveys (and thus inhomogeneous sample) to characterize the intervening galaxies and quasars. Studies that have used CCDs have looked only on very small scales and therefore are likely not sampling the galaxy background well.

We have embarked on a survey of galaxies in the vicinity of ~100 quasars that are bright both in the radio ( S5GHz > 1Jy ) and the optical (V < 20 ) to search for this angular correlation signal. We use the KPNO Schmidt telescope with its 69' x 69' field of view. In addition, 20 `control' fields not known to harbor bright quasars have also been included in the survey in order to accurately sample the galaxy number density background.

Presented here is a small subsample of that survey. We report on the analysis of 24 quasar fields and 7 control fields. These quasar fields have been chosen to have the highest potential for evidence of this weak lensing effect. Currently with our small statistics, we find only a marginal overdensity of galaxies around these quasars. We discuss our findings in the contexts of the larger body of work on the subject and cosmological implications.

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