A Narrowband Imaging Search for [Oiii] Emission from Galaxies atz > 3

We present the results of a narrow-band survey of QSO fields at redshiftsthat place the [OIII](5007) emission line in the 1% 2.16micron filter. We haveobserved 3 square arcminutes and detected one emission line candidate object inthe field around PC 1109+4642. We discuss the possibilities that this object isa star-forming galaxy at the QSO redshift, z_em=3.313 or a Seyfert galaxy. Inthe former case, we infer a star formation rate of 170 Msun/yr for thisKprime=21.3 object. The galaxy has a compact but resolved morphology, with aFWHM=0.6arcs, or 4.2kpc at z=3.313 (H_0=50 km/s/Mpc and q_0=0.5). The comovingdensity of such objects in QSO environments appears to be 0.0033Mpc^3,marginally lower (<= 3sigma) than the density observed for Halpha-emitters inabsorption-line fields at z~2.5, but similar to the density of Lyman BreakGalaxies at z~3. If on the other hand, most of the line emission is [OIII] froma Seyfert 2 nucleus at z=3.31, then the high inferred volume density couldimply a large evolution in the Seyfert 2 luminosity function from the currentepoch. We find the field containing the object to also contain many faintextended objects in the Kprime image, but little significant excess over theexpected number-magnitude relation. We discuss the implication of the emissionline being a longer wavelength line at a lower redshift.Comment: 19 pages, including 4 figures, accepted for publication by Ap