Distant galaxy clusters identified from optical background fluctuations

We present the first high-redshift (0.3 < z < 1.1) galaxy clusters found by systematically identifying optical low surface brightness fluctuations in the background sky. Using spectra obtained with the Keck I telescope and I-band images from the Palomar 1.5 m telescope, we conclude that at least eight of the 10 candidates examined are high-redshift galaxy clusters. The identification of such clusters from low surface brightness fluctuations provides a complement to classic selection methods based on overdensities of resolved galaxies and enables us to search efficiently for rich high-redshift clusters over large areas of the sky. The detections described here are the first in a survey that covers a total of nearly 140 deg² of the sky and should yield, if these preliminary results are representative, over 300 such clusters.