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P. Palunas (NASA/GSFC & CUA), P. Francis (MSSSO), B. Woodgate (NASA/GSFC)
We detect an overdensity of emission-line objects concentrated in a 40\times 10 arcmin2 region coincident with the z=2.38 cluster of galaxies toward J2142.4-4420 (also known as the Francis cluster). The Francis cluster consists of a region of a neutral hydrogen extending at least 8\arcmin\ and three strong Ly\alpha emitters. The new emission-line detections suggest that the cluster is embedded in a much larger structure which may correspond to a filament or cross-section of a great wall at least 40\times 10~Mpc in transverse extent.
The objects were detected in a narrowband filter of bandpass 55~Å\ using the Mosaic camera on the CTIO 4m telescope. The strong emission at 4110 Å\ (> 100 Å\ equivalent width) argue for the objects being Ly\alpha emitters at z=2.38, and thus physically associated with the cluster. The volume probed by the narrowband filter and the [OII] equivalent-widths required argue strongly against a significant contamination of our sample by interlopers at z=0.103.
This study was funded by a NASA grant NRA--98--03--UVG--011. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation.