THE THETA-Z RELATION FOR HST BULGES AND DISKS OUT TO Z-SIMILAR-OR-EQUAL-TO-0.8

We present HST scale lengths and ground-based redshifts for 63 faint field galaxies down to I less-than-or-similar-to 21.5 mag from the Medium-Deep Survey. These have measured redshifts z less-than-or-similar-to 0.8 and half-light radii 0''.1 less-than-or-similar-to r(e), r(s) less-than-or-similar-to 5''. We present the THETA-z relation for r1/4-bulges and exponential disks separately for world models with q0 = 0.0-1.0. We show that selection against low surface brightness galaxies in the HST images and ground-based spectra is comparable to that in local surveys. We compare our HST disk-dominated galaxies to a magnitude-limited subsample of the ESO-Uppsala local spirals. Extrapolating the best-fit local exponential disk scale length (r(s) = 3.5 kpc for H0 = 75) out to z = 0.8, we find a rather symmetrical distribution of HST disks around this value. This implies that galaxy disks have been stable since z congruent-to 0.8. We compare our HST bulge-dominated galaxies with r1/4-profiles to a magnitude-limited subsample of local Seven Samurai ellipticals. The latter have a local best fit r(e) = 5.7 kpc. Our HST bulge sample shows a similar distribution for z less-than-or-similar-to 0.8. Elliptical galaxy scale lengths have thus also remained rather constant since z less-than-or-equal-to 0.8. We set limits to their possible evolution.