Keck spectroscopy and NICMOS photometry of a redshift z=5.60 galaxy

We present Keck Low Resolution Imaging Spectrometer spectroscopy along with Near-Infrared Camera and Multiobject Spectrometer (NICMOS) F110W (similar to J) and F160W (similar to H) images of the galaxy HDF 4-473.0 in the Hubble Deep Field (HDF), with a detection of an emission Line consistent with Ly alpha at a redshift of z = 5.60. Attention to this object as a high-redshift galaxy was first drawn by Lanzetta, Yahil, & Fernandez-Soto and appeared in their initial list of galaxies with redshifts estimated from the Wide Field Planetary Camera 2 (WFPC2) HDF photometry. It was selected by us for spectroscopic observation, along with others in the HDF, on the basis of the NICMOS F110W and F160W and WFPC2 photometry. For H-0 = 65 km s(-1) Mpc(-1) and q(0) = 0.125, the use of simple evolutionary models along with the F814W (similar to I), F110W, and F160W magnitudes allow us to estimate the star formation rate (similar to 13 M. yr(-1)). The colors suggest a reddening of E(B - V) similar to 0.06. The measured flux in the Lya line is approximately 1.0 x 10(-17) ergs cm(-2) s(-1), and the rest-frame equivalent width, correcting for the absorption caused by intervening H I, is similar to 90 Angstrom. The galaxy is compact and regular, but resolved, with an observed FWHM of similar to 0." 44. Simple evolutionary models can accurately reproduce the colors, and these models predict the Ly alpha flux to within a factor of 2. Using this object as a template shifted to higher redshifts, we calculate the magnitudes through the F814W and two NICMOS passbands for galaxies at redshifts 6 < z < 10.