A narrow-band search for Ly alpha emitting galaxies at z=8.8

Aims. The first star forming galaxies in the early universe should be copious Ly alpha emitters and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that the luminosity function of Ly alpha emitting galaxies beyond z similar to 6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Ly alpha emitters at redshift 8.8. Methods. 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 similar to 1.3 x 10(-17) erg s(-1) cm(-2) (respectively similar to 1.3 x 10(43) erg s(-1)) in a narrow band filter centered in a region of low OH sky emission at 1.19 mu m. Candidate Ly alpha emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. Results. No z = 8.8 Ly alpha emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at z similar to 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.