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 [ OII ] \lambda 3727Å emission line galaxies to date .
The images reach an emission line flux limit ( 5 \sigma ) of 1.5 \times 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 [ OII ] \lambda 3727Å emission line objects at redshift z \sim 1.85 in a co-moving volume of \sim 4100 Mpc ^ { 3 } .
Objects are selected using an observed equivalent width ( EW _ { obs } ) threshold of EW _ { obs } > 50Å .
The sample is used to derive the space density and constrain the luminosity function of [ OII ] emitters at z =1.85 .
We find that the space density ( \rho ) of objects with observed [ OII ] luminosities in the range log ( L _ { [ OII ] } ) > 41.74 erg s ^ { -1 } is log ( \rho ) = - 2.45 \pm 0.14 Mpc ^ { -3 } , a factor of 2 greater than the observed space density of [ OII ] emitters reported at z \sim 1.4 .
After accounting for completeness and assuming an internal extinction correction of A _ { H \alpha } =1 mag ( equivalent to A _ { [ OII ] } =1.87 ) , we report a star formation rate density of \dot { \rho } _ { * } \sim 0.38 \pm 0.06 M _ { \odot } yr ^ { -1 } Mpc ^ { -3 } .
We independently derive the dust extinction of the sample using 24 \mu m fluxes and find a mean extinction of A _ { [ OII ] } =0.98 \pm 0.11 magnitudes ( A _ { H \alpha } =0.52 ) .
This is significantly lower than the A _ { H \alpha } =1 ( A _ { [ OII ] } =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 \dot { \rho } _ { * } \sim 0.24 \pm 0.06 M _ { \odot } yr ^ { -1 } Mpc ^ { -3 } .