2012MNRAS.426.2178B

We present the results of a high-redshift, z = 4.6, survey of [OII]λ3727 emission line galaxies in the GOODS-S field. The survey uses deep near-infrared data in the NB2090 (λ_c= 2.095 µm, Δ λ = 0.02 µm) and Ks (λ_c= 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 x 10^–18erg/scm ^–2. At z = 4.6, the survey probes a comoving volume of ∼ 6680Mpc³.

Three [OII] emission line candidates at z ∼ 4.6 are selected using the Lyman-break criteria. Photometric redshift analysis supports the conclusion that these are genuine [OII] 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 [OII] emitters and secondly, only the most likely candidate is a genuine [OII] emitter.

We use the line fluxes of these objects to place confidence limits on the star formation rate density (SFRD) in bright (log(\mi L\mo [\mi O\mspace\mi ii\mo ]\mo)\mo >\mn 42.0\mo ) [OII] emission line galaxies. Assuming an observed [OII]/Hα line ratio of 0.45 and A(Hα) = 1.0mag, we report an SFRD of rhodot\mo *\mo (\mo log\mo (\mi L\mo [\mi O\mspace\mi ii\mo ]\mo )\mo >\mn 42.0\mo)\mn 0.058\mspace\mi M\mspace \mi yr=–\mn 1\mspace\mi Mpc =–\mn 3 in our objects. Using small number statistics, we then place a 50 per cent confidence interval on the global star formation rate of rho=dot=*=(=log=(\mi L=[\mi O\mspace \mi ii=]=)=>\mn 42.0=)==\mn 0.058=±\mn 0.013\mspace\mi M\mspace\mi yr=–\mn 1\mspace\mi Mpc=–\mn 3. By combining our results with those from low-z surveys, we compile the first homogeneous set of measurements of the SFRD in bright [OII] emitters from z = 0 to 4.6. From this, we conclude that there was an increase in the SFRD in the brightest [OII] emitters of at least a factor of 2 between z = 4.6 and 1.85.