[O ii] emitters at z ∼ 4.6 in the GOODS field: a homogeneous measure of evolving star formation


E-mail: kdb25@ast.cam.ac.uk


We present the results of a high-redshift, z = 4.6, survey of [O ii] λ3727 emission line galaxies in the GOODS-S field. The survey uses deep near-infrared data in the NB2090 (λc = 2.095  μm, Δ λ = 0.02 μm) and Ks (λc = 2.146  μm, Δ λ = 0.324 μm) filters taken with the European Southern Observatory instrument, HAWK-I. The images reach an emission line flux limit (5σ) of 3.16 × 10−18 erg s−1 cm −2. At z = 4.6, the survey probes a comoving volume of ∼6680 Mpc3.

Three [O ii] emission line candidates at z ∼ 4.6 are selected using the Lyman-break criteria. Photometric redshift analysis supports the conclusion that these are genuine [O ii] emitters, ruling out a z < 3 solution entirely for one of the candidates. In the analysis presented in this paper, two scenarios are considered: first, all three candidates are genuine [O ii] emitters and secondly, only the most likely candidate is a genuine [O ii] emitter.

We use the line fluxes of these objects to place confidence limits on the star formation rate density (SFRD) in bright (log(math formula [O ii] emission line galaxies. Assuming an observed [O ii]/Hα line ratio of 0.45 and A(Hα) = 1.0 mag, we report an SFRD of math formula in our objects. Using small number statistics, we then place a 50 per cent confidence interval on the global star formation rate of math formula. By combining our results with those from low-z surveys, we compile the first homogeneous set of measurements of the SFRD in bright [O ii] emitters from z = 0 to 4.6. From this, we conclude that there was an increase in the SFRD in the brightest [O ii] emitters of at least a factor of 2 between z = 4.6 and 1.85.