[O ii] emitters in the GOODS field at z ∼ 1.85: a homogeneous measure of evolving star formation

We present the results of a deep, near-infrared, narrow-band imaging survey at a central wavelength of 1.062 mu m (FWHM = 0.01 mu m) in the GOODS-South field using the ESO VLT instrument, HAWK-I. The data are used to carry out the highest redshift search for [O ii] lambda 3727 A emission line galaxies to date. The images reach an emission line flux limit (5 Sigma) of 1.5 x 10-17 erg cm-2 s-1, additionally making the survey the deepest of its kind at high redshift. In this paper we identify a sample of [O ii] lambda 3727 A emission line objects at redshift z similar to 1.85 in a comoving volume of similar to 4100 Mpc-3. Objects are selected using an observed equivalent width (EWobs) threshold of EWobs > 50A. The sample is used to derive the space density and constrain the luminosity function of [O ii] emitters at z = 1.85. We find that the space density () of objects with observed [O ii] luminosities in the range is log() = -2.45 +/- 0.14 Mpc-3, a factor of 2 greater than the observed space density of [O ii] emitters reported at z similar to 1.4. After accounting for completeness and assuming an internal extinction correction of A(H alpha) = 1 mag (equivalent to = 1.87), we report a star formation rate density of M-circle dot yr-1 Mpc-3. We independently derive the dust extinction of the sample using 24-mu m fluxes and find a mean extinction of magnitudes (A(H alpha) = 0.52). This is significantly lower than the A(H alpha) = 1 ( = 1.86) mag value widely used in the literature. Finally, we incorporate this improved extinction correction into the star formation rate density measurement and report M-circle dot yr-1 Mpc-3.