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 (λ = 5390 Å, Δλ = 77 Å) and multicolor observations of the Hubble Deep Field and the Hawaii Deep Field SSA 22 obtained with the LRIS instrument at the 10 m Keck II Telescope. It is shown that there is a substantial population of galaxies at z ∼ 3.4 that can be selected by Lyα 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 Lyα, 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 H₀ = 65 km s^-1 Mpc^-1 and q₀ = 0.5 in the Lyα-selected objects, though the value could be substantially higher if there is significant extinction.