Lyman Alpha Imaging of a Proto–cluster Region At

We present very deep narrow band observations of a volume containing a significant over-density of galaxies previously discovered in our survey for continuum–selected Lyman break galaxies at redshifts 2.7 < ∼ z < ∼ 3.4. The new observations are used in conjunction with our spectroscopic results on LBGs to compare the effectiveness of continuum and emission line searches for star forming galaxies at high redshift, and to attempt to extend the search for members of the structure at 〈z〉 = 3.09 to much fainter continuum luminosities. The 8′.7 by 8′.9 field contains a very high surface density of emission line candidates, approximately 6 times higher than in published blind narrow–band searches to comparable depth and at similar redshift. This level of density enhancement for the 〈z〉 = 3.09 structure is consistent with that inferred from the analysis of the spectroscopic Lyman break galaxy sample in the same region (6.0± 1.2), but extends to continuum luminosities up to 2 magnitudes fainter. We find that only ∼ 20 − 25% of all galaxies at a given UV continuum luminosity would be flagged as narrow–band excess objects subject to the typical limits Wλ > 80 Å in the observed frame. The remainder have lines that are too weak (< 20 Å rest equivalent width) to make selection by narrow–band excess effective. There is no evidence for a significantly higher fraction of large Lyman α line equivalent widths at faint continuum luminosities. We have also discovered two extremely bright, large, and diffuse Lyman α emitting “blobs”, which are apparently associated with, but not centered on, previously known Based on data obtained at the Palomar Observatory and the W.M. Keck Observatory. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was was made possible by the generous financial support of the W.M. Keck Foundation. NSF Young Investigator