FLEX: the first light explorer. A fully OH-suppressed near-infrared integral field spectrograph

FLEX is a concept for a fully OH suppressed near infrared integral field spectrograph, being developed at the AAO.FLEX will be the first instrument to employ fibre Bragg gratings for OH suppression, a radical new technology which cleanly suppresses the atmospheric OH emission lines at 30dB whilst maintaining a high overall throughout of ~90%. In this paper we simulate the expected performance of FLEX, and discuss its impact on the science case. FLEX will effectively make the near-infrared sky 4 mags fainter in the H band and 3 mags fainter in the J band, offering unprecedentedly deep views of the near-infrared Universe. The FLEX concept is optimised for the identification of the sources of first light in the Universe - high redshift galaxies or quasars identified through Lyman-alpha emission or a Lyman break in the continuum spectrum. As such it will consist of a 2x2" integral field unit, composed of a 61 lenslet hexagonal array, feeding an existing moderate spectral resolution spectrograph, via an OH-suppression unit. We have simulated the performance of FLEX and show that it can provide robust identification of galaxies at the epoch of reionisation. A FLEX-like instrument on an ELT could measure the ionisation and enrichment of the inter-galactic medium beyond a redshift of 7 via metal absorption lines.