A Narrowband Imaging Search for [OIII] Emission from Galaxies at z>3

We present the results of a narrow-band survey of QSO fields at redshifts that place the [OIII](5007Å) emission line in the ∆λ λ ∼ 1% 2.16 μm filter. We have observed 3 square arcminutes and detected one emission line candidate object in the field around PC 1109+4642. We discuss the possibilities that this object is a star-forming galaxy at the QSO redshift, zem = 3.313 or a Seyfert galaxy. In the former case, we infer a star formation rate of 170M⊙/yr for this K=21.3 object. The galaxy has a compact but resolved morphology, with a FWHM=0.6, or 4.2kpc at z=3.313 (H0 = 50 km s Mpc and q0 = 0.5). The comoving density of such objects in QSO environments appears to be 0.0033Mpc, marginally lower (≤ 3σ) than the density observed for Hα-emitters in absorption-line fields at z∼ 2.5, but similar to the density of Lyman Break Galaxies at z∼3. If on the other hand, most of the line emission is [OIII] from a Seyfert 2 nucleus at z=3.31, then the high inferred volume density could imply a large evolution in the Seyfert 2 luminosity function from the current epoch. We find the field containing the object to also contain many faint extended objects in the K image, but little significant excess over the expected number-magnitude relation. We discuss the implication of the emission line being a longer wavelength line at a lower redshift. Subject headings: cosmology : observation — galaxies : evolution — infrared : galaxies