An Infrared Search for Star-forming Galaxies at z > 2

We report the cumulative results of an ongoing near-infrared search for redshifted Hα emission from normal galaxies at z > 2. An infrared search reduces the bias due to reddening. Using narrowband imaging with the Near Infrared Camera on the Keck I 10 m telescope, a survey area of almost 12 arcmin2 has been covered. Target regions were selected by matching the redshifts of QSO emission and metal-line absorptions to our available filters. The survey depth is 7 × 10-17 ergs cm-2 s-1 (3 σ) in Hα and K' ≃ 22. Eleven Hα emitters plus two Seyfert I objects have been discovered. The high density of galaxy detections, corresponding to a comoving volume density of 0.0135±0.00550.0035 Mpc-3, makes it unlikely that all of the Hα flux in these objects is the result of active nuclei. There is a strong suggestion of clustering in the environments of metal-line absorbers. Each candidate galaxy lies typically within a projected distance of 250 kpc of the QSO line of sight and is resolved but compact. The average star formation rate inferred for the galaxies from the Hα flux is 50 M☉ yr-1, significantly higher than present-day star-forming galaxies but consistent with other estimates for galaxies at high redshift.