2007A&A...461..911C

The first star forming galaxies in the early universe should be copious Lyα emitters and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that the luminosity function of Lyα emitting galaxies beyond z∼6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Lyα emitters at redshift 8.8. We performed a narrow band imaging programme using ISAAC at the ESO VLT. Seven fields, covering a total area of 31 sq. arcmin and for which optical and broad band infra-red images have been obtained in the GOODS survey, were imaged to a limiting flux (respectively luminosity) of ∼1.3x10^–17erg/s/cm2 (respectively ∼1.3x10⁴³erg/s) in a narrow band filter centered in a region of low OH sky emission at 1.19µm. Candidate Lyα emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. No z=8.8 Lyα emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at z∼6. Our results do suggest, however, that detections or substantial constraints could be achieved by this method in the near future with larger field instruments planned for various telescopes.