Based on our high-quality ACS images in the i-and-z-bands and deep ground-based infrared images of twelve clusters, we found a number z-band dropout objects. They exhibit a large z-J color decrement and a flat infrared color (J-H or J-K) and are believed to be field galaxies at redshift 7-8. Some of these z-band dropout sources, at approximately AB=24, are considerably brighter than those found in the GOODS and UDF, probably as the results of significant amplification by the clusters. We are carrying out spectroscopic followup observations of the brightest candidates, to search for their narrow Ly-alpha emission line feature.
This research is supported by NASA grant NAG5-7697. \
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