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

Abstract

We report the cumulative results of an on-going near-infrared search for redshifted H-alpha emission from normal galaxies at z>2. An infrared search reduces the bias due to reddening. Using narrow-band imaging with the Near Infrared Camera on the Keck I 10-m telescope, a survey area of almost 12 square arcminutes 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 7E-17 ergs/cm^2/s (3sigma) in H-alpha and K-prime ~22. Eleven H-alpha-emitters, plus two Seyfert I objects, have been discovered. The high density of galaxy detections, corresponding to a co-moving volume density of 0.0135/Mpc^3, makes it unlikely that all of the H-alpha 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 250kpc of the QSO line of sight and is resolved but compact. The average Star Formation Rate inferred for the galaxies from the H-alpha flux is 50 Msun/yr, significantly higher than current day star-forming galaxies, but consistent with other estimates for galaxies at high redshift.