A z = 5.34 galaxy pair in the Hubble deep field

We present spectrograms of the faint V-drop (V-606 = 28.1, I-814 = 25.6) galaxy pair HDF 3-951.1 and HDF 3-951.2 obtained at the Keck II Telescope. In a recent study, Fernandez-Soto, Lanzetta, & Yahil derive a photometric redshift of z(ph) = 5.28(-0.41)(+0.34) (2 sigma) for these galaxies; our integrated spectrograms show a large and abrupt discontinuity near 7710 +/- 5 Angstrom. This break is almost certainly due to the Ly alpha forest because its amplitude (1 - f(v)(short)/f(v)(long) > 0.87, 95% confidence limit) exceeds any discontinuities observed in stellar or galactic rest-frame optical spectra. The resulting absorption break redshift is z = 5.34 +/- 0.01. Optical/near-IR photometry from the HDF yields an exceptionally red (V-606-I-814) color, consistent with this large break. A more accurate measure of the continuum depression blueward of Lya utilizing the imaging photometry yields D-A = 0.88. The system as a whole is slightly brighter than L*(1500) relative to the z similar to 3 Lyman break population, and the total star formation rate inferred from the UV continuum is approximate to 22 h(50)(-2) M-. yr(-1) (q(0) = 0.5) assuming the absence of dust extinction. The two individual galaxies are quite small (size scales less than or similar to 1 h(50)(-1) kpc). Thus these galaxies superficially resemble the "building blocks" of Pascarelle and coworkers; if they comprise a gravitationally bound system, the pair will likely merge in a timescale similar to 100 Myr.