Searching for High-Redshift Lyman Alpha Emitters in the COSMOS Field with NEWFIRM
(19 votes over all institutions)
The study of Lya emission in the high-redshift universe is a useful probe of the epoch of reionization, as the Lya line should be attenuated by the intergalactic medium (IGM) if the local neutral hydrogen fraction is over 50%. Here we present the results of a deep and wide imaging search for Lya emitters in the COSMOS field. We have used two ultra-narrowband filters (filter widths of ~8 and 9 {\deg}A) on the NEWFIRM camera, installed on the Mayall 4m telescope at Kitt Peak National Observatory, in order to isolate Lya emitters at z = 7.7; such ultra-narrowband imaging searches have proved to be excellent at detecting Lya emitters. We found 5sigma detections of four candidate Lya emitters in a survey volume of 2.8 x 104 Mpc3. Each candidate has a line flux greater than 8 x 10-18 erg s-1 cm-2. Using these results to construct a luminosity function and comparing to previously established Lya luminosity functions at z = 5.7 and z = 6.5, we find no conclusive evidence for evolution of the luminosity function between z = 5.7 and z = 7.7. Statistical Monte Carlo simulations suggest that half of these candidates are real z = 7.7 targets, and spectroscopic followup will be required to verify the redshift of these candidates. However, our results would suggest no major evolution in the neutral hydrogen fraction of the IGM between redshift z = 3.1 and z = 7.7, even if only one or two of the z = 7.7 candidates are spectroscopically confirmed.
