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We present 18 spectra, obtained with the Keck 10m telescope, of faint fieldgalaxies (19 $<$ I $<$ 22, 0.2 $<$ z $<$ 0.84) previously imaged by {\it HST's}WFPC2. Though small, our sample appears to be representative of field spiralswith a magnitude--limit of I $\le$ 22. Combining the results from the spectraland imaging data, we have derived various quantitative parameters for thegalaxies, including colors, inclinations, emission line equivalent widths,redshifts, luminosities, internal velocity information and physical scalelengths. In particular, disk scale lengths (with sizes ranging from $\sim$1--5kpc) have been measured from fits to the surface brightness profiles. We havealso measured internal velocities with a rest frame resolution of $\sigma$ = 55to 80 km s$^{-1}$ by fitting to the emission lines. The luminosity--disk sizeand luminosity--internal velocity (Tully--Fisher) relations for our moderateredshift galaxies are similar to the scaling relations seen for local galaxies,albeit with a modest brightening of $\sim$1 magnitude. The one bulge--dominatedgalaxy in our sample (at z = 0.324) has a relatively blue color, reveals weakemission lines and is $\sim$0.5 magnitude brighter in the rest frame thanexpected for a passive local elliptical. Our data suggest that galaxies atabout half the age of the Universe have undergone mild luminosity evolution tothe present epoch, but are otherwise quantitatively similar to galaxies seenlocally.

Keck Spectroscopy and Hubble Space Telescope Imaging of Field Galaxies at Moderate Redshift