The Luminosity Function of Ly Emitters at Redshiftz~5.7

We report results of a deep wide-field narrowband survey for redshift z~5.7Ly alpha emitters carried out with SuprimeCam on Subaru 8.3-m telescope. Deepnarrowband imaging of the SSA22 field through a 120 A bandpass filter centeredat 8150 A was combined with deep multicolor RIz' SuprimeCam broadband imaging,and BVRZ imaging taken with CFHT's CFH12K camera to select high-redshift galaxycandidates. Spectroscopic observations were made using the new wide-fieldmulti-object DEIMOS spectrograph on Keck for 22 of the 26 candidate objects.Eighteen objects were identified as z~5.7 Lyman alpha emitters, and a furthernineteenth candidate was identified based on an LRIS spectrum. At the 3.3 Aresolution of the DEIMOS spectra the asymmetric profile for Ly alpha emissionwith its steep blue fall-off can be clearly seen. We use this to describe thedistribution of equivalent widths and the continuum color break properties forz~5.7 Ly alpha galaxies compared with foreground objects. The large majority(>75%) of Ly alpha lines have rest frame equivalent widths less than 240 A andcan be understood in terms of young star forming galaxies with a Salpeterinitial mass function for the stars. With narrowband selection criteria of I-N> 0.7 and N<25.05 (AB mags) we find a surface density of Ly alpha emitters of0.03 per square arcminute per (deltaz=0.1) to a limiting flux just under 2e-17erg/cm2/s. The luminosity function of the Ly alpha emitters is similar to thatat lower redshifts to the lowest measurable luminosity of 1e43 ergs/s as is theuniversal star formation rate based on their continuum properties. We note thatthe objects are highly structured in both spatial and spectral properties onthe angular scale of the fields (~60 Mpc), and that multiple fields will haveto be averaged to accurately measure their ensemble properties.