A proposal for finding clusters of galaxies at z greater than or similar to 1

At large redshifts, a cluster or group may be too distant for the galaxies within the cluster to be detected individually in a short exposure. However, the light from these ''undetected'' galaxies still modulates the surface brightness of the background sky. Distant clusters can appear as 10 ''-1'.5 sized fluctuations in the surface brightness of the extragalactic background light (EBL). The fluctuations have central surface brightnesses fainter than roughly 26 mag arcsec(-2) (in V) for clusters with z greater than or similar to 1 and are brighter than the random fluctuations produced by held galaxies on comparable angular scales. While such low surface brightnesses features are difficult to detect with direct high-resolution imaging, we demonstrate that they are easily reached in short exposures through smoothing the sky in very flat CCD images. For a reasonable extrapolation of the properties and space densities of clusters and groups and for a wide range of cosmological assumptions, we find that there should be tens of high-redshift dusters per square degree visible in the optical extragalactic background. Therefore, searching for small bright fluctuations in the EBL could be an efficient method for identifying high-redshift cluster candidates. The detection rate is sensitive to the rate of cluster and galaxy evolution and may vary between 1 and 100 clusters per square degree. With follow-up imaging and spectroscopy of the cluster candidates, one can constrain both galaxy luminosity evolution and duster mass evolution, and potentially discriminate between different cosmological models.