PI: Sangeeta Malhotra, The Johns Hopkins University, firstname.lastname@example.org
Address: 3400 N. Charles Street, Baltimore, MD 21218, USA
CoI: James Rhoads, Space Telescope Science Institute
Title: Catching them Young: Galaxies at z=6.6
Abstract: The formation of galaxies and the reionization of the intergalactic medium are crucial milestones in cosmic history that are only now becoming accessible to observation. \lya emission from star-forming galaxies offers a powerful probe of both. \lya line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in galaxies with young stars and little or no dust - properties expected in galaxies undergoing their first burst of star- formation. The Large Area Lyman Alpha survey at NOAO has succesfully found large samples of \lya galaxies at z=4.5 and 5.7 . We now want to extend this survey to z=6.6 for two main reasons: (1) The recent identification of a quasar at z=6.28 shows that galaxy formation was well underway at z>6. So we can push \lya searches to higher redshifts to find earlier generations of young galaxies. This should give us a direct picture of the evolution of the youngest galaxies over (Delta) z ~ 2.2. (2) The Gunn-Peterson trough seen in spectra of z \ge 5.7 quasars suggests that reionization occurred as recently as \zre \la 6. However, these spectra only provide optical depth limits of (tau) \ga 5, while a neutral universe would give (tau) ~ 10^5. \lya source counts will break this degeneracy and provide an independent test of reionization: If (tau) ~ 10^5, we will see a sharp decrease in the counts at z=6.6 because \lya photons are resonantly scattered in neutral gas, rendering the sources too diffuse to be detected. A deep narrowband search at 9200Aexploits the last available optical window for a sensitive and efficient \lya search at z=6.6. The Mosaic camera on the Mayall telescope optimizes the area and depth of the survey. So we expect to find 10-75 \lya emitters, unless \zre < 6.6. This is a large enough sample that if do \it not find any \lya emitters, we will have measured the epoch of reionization, and if we \it do find them then we can study the evolution of the youngest galaxies at the earliest epochs probed so far.
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