Bright Lyα emitters at z ~ 9 : Constraints on the LF from HizELS

Abstract

New results are presented, as part of the Hi-z Emission Line Survey (HizELS), from the largest area survey to date (1.4 deg ) for Lyα emitters (LAEs) at z ~ 9. The survey, which is primarily targeting Hα emitters at z <3, uses the Wide Field CAMera on the United Kingdom Infrared Telescope and a custom narrow-band filter in the J band and reaches a Lyα luminosity limit of ~10 ergs over a co-moving volume of 1.12 × 10 Mpc at z = 8.96 ± 0.06. Only two candidates were found out of 1517 line emitters and those were rejected as LAEs after follow-up observations. The limit on the space density of bright LAEs is improved by three orders of magnitude, consistent with suppression of the bright end of the Lyα luminosity function beyond z ~ 6. Combined with upper limits from smaller but deeper surveys, this rules out some of the most extreme models for high-redshift LAEs. The potential contamination of future narrow-band Lyα surveys at z > 7 by Galactic brown dwarf stars is also examined, leading to the conclusion that such contamination may well be significant for searches at 7.7 <z <8.0, 9.1 <z <9.5 and 11.7 <z <12.2.