ZEN and the search for high-redshift galaxies

We present the ZEN (z equals nine) survey: a deep, narrow J-band search for proto-galactic Ly α emission at redshifts z ∼ 9. In the first phase of the survey, dubbed ZEN1, we combine an exceptionally deep image of the Hubble Deep Field South, obtained using a narrow-band filter centred on the wavelength 1.187 μm, with existing deep, broad band images covering optical to near infrared wavelengths. Candidate z ∼ 9 Ly α-emitting galaxies display a significant narrow-band excess relative to the Js-band that are undetected at optical wavelengths. We detect no sources consistent with this criterion to the 90% point source flux limit of the NB image, FNB = 3.28 × 10−18 ergs s−1 cm−2. The survey selection function indicates that we have sampled a volume of approximately 340 h−3 Mpc3 to a Ly α emission luminosity of 1043 h−2 ergs s−1. When compared to the predicted properties of z ∼ 9 galaxies based upon no evolution of observed z ∼ 6 Ly α-emitting galaxies, the 'volume shortfall' of the current survey, i.e., the volume required to detect this putative population, is a factor of at least 8-10. We also discuss continuing narrow J-band imaging surveys that will reduce the volume shortfall factor to the point where the no-evolution prediction from z ∼ 6 is probed in a meaningful manner.