First Investigation of the Clustering Environment of Damped Lyα Absorbers at z ≃ 4

Abstract

We report the first observations of the clustering environment of damped Lyman α absorption systems at z~=4. Color selection and photometric redshifts were used to select 44 candidate Lyman-break galaxies brighter than IAB=25.5 from deep BRI images of the 35 arcmin2 field containing the quasar BR 0951-04. Multislit spectroscopy of 35 candidate galaxies was performed and eight of these candidates have been confirmed as z>3.5 Lyman-break galaxies. With only BRI photometry, the photometric redshifts are quite accurate for the spectroscopically confirmed galaxies but have a high rate of misclassification due to color degeneracies between Lyman-break galaxies and low-redshift ellipticals. Both of the z>3.5 galaxies found within 15" of the quasar line-of-sight appear to be causing absorption systems in the quasar spectrum. We use a battery of statistical tests to look for clustering in the redshift histogram of the z>3.5 galaxies but do not find measurable clustering of these Lyman-break galaxies with the damped Lyα absorbers. With a larger sample of galaxies, our method should determine the cross-correlation between these objects, which probes the bias and hence the mass of the damped Lyα absorbers. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the University of California, the California Institute of Technology, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.