High-z Lyα 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 SSA 22

We present deep narrowband (lambda = 5390 Angstrom, Delta lambda = 77 Angstrom) and multicolor observations of the Hubble Deep Field and the Hawaii Deep Field SSA 22 obtained with the LRIS instrument at the 10 m Keek II Telescope. It is shown that there is a substantial population of galaxies at z similar to 3.4 that 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 initial mass function, we estimate a minimum star formation rate of 0.01 M. Mpc(-3) yr(-1) at z = 3.4 for H-0 = 65 km s(-1) Mpc(-1) and q(0) = 0.5 in the Ly alpha-selected objects, though the value could be substantially higher if there is significant extinction.