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# Proposal Information for 2008B-0500

Address: School of Earth and Space Exploration, PO Box 871404, Tempe, AZ 85287, USA

CoI: Sangeeta Malhotra, Arizona State University
CoI: Sylvain Veilleux, U. Maryland
CoI: Steven Finkelstein, Arizona State University
CoI: Ilian Iliev, ETH Zurich
CoI: Buell Jannuzi, NOAO
CoI: Bahram Mobasher, UC Riverside
CoI: Norbert Pirzkal, STScI
CoI: Ron Probst, NOAO
Abstract: Lyman alpha emitting galaxies offer a powerful probe of reionization history: The intergalactic medium will obscure Lyman alpha from view if the neutral fraction exceeds ~ 30%. This complements the Gunn- Peterson test (which saturates at neutral gas fraction of about 1%), and the microwave background polarization measurements (which provide an integral constraint on the ionized gas column, but no detailed history of reionization). We have applied this test to show that the IGM is predominantly ionized at z=6.5 (Malhotra & Rhoads 2004, 2006). However, the CMBR polarization suggests a characteristic'' redshift z=10.8. We will use NEWFIRM to obtain \lya galaxy constraints on the IGM neutral fraction at z~ 9. \it This probes the most interesting range of redshift space, where the CMBR constraint suggests a substantial neutral fraction. With five nights on NEWFIRM, we should reach sufficient depth to either (a) detect \lya galaxies or (b) demonstrate evolution of either the \lya luminosity function or IGM neutral fraction between z=6.5 and z=9. In the case of a neutral IGM, the lines are preferentially attenuated, and the sources will show lower equivalent widths.