High-z Lyman-alpha Emitters. I. A Blank-Field Search for Objects Near   Redshift z=3.4 in and around the Hubble Deep Field and the Hawaii Deep Field   SSA22
  We present deep narrow-band (lambda = 5390 Angstroms, delta lambda = 77 Angstroms) and multi-color observations of the Hubble Deep Field and the Hawaii Deep Field SSA22 obtained with the LRIS instrument at the Keck II 10-m telescope. It is shown that there is a substantial population of galaxies at z~3.4 which can be selected by Ly alpha emission. Comparison with color-selected samples shows that the samples selected with these different criteria have substantial, but not complete overlap, and that there is a comparable surface density in the two selected populations. The emission-line selected samples include objects with strong Ly alpha, and which are significant contributers to the integrated star formation at these epochs. For a Salpeter IMF we estimate a minimum star formation rate of 0.01 solar masses per cubic Mpc per yr at z=3.4 for H_0 = 65 km/s/Mpc and q_0 = 0.5 in the Ly alpha-selected objects, though the value could be substantially higher if there is significant extinction. 
Lennox L. Cowie and Esther M. Hu (Univ. of Hawaii, Institute for   Astronomy)