GALAXY SURFACE BRIGHTNESS AND SIZE EVOLUTION TO Z-SIMILAR-TO-4

Using HST WFPC2 data, we estimate half-light radii, morphological clas sifications and rest-frame, blue-band absolute magnitudes for 270 gala xies with spectroscopic redshifts from z similar to 0 to z=3.43, and 7 7 thought from their colours to be at 2.0 less than or equal to z less than or equal to 4.5. The mean blue-band surface brightness decreases by similar to 2 mag along the Hubble sequence from ellipticals to irr egulars, but peculiar galaxies (forming similar to 21 per cent of the sample) tend to have blue colours but a high surface brightness. The m ean rest-frame, blue-band surface brightness increases by 0.95+/-0.22 mag between z(mean)similar or equal to 0.2 and z(mean)similar or equal to 0.9 redshift intervals, with similar evolution for all the morphol ogical types. We estimate that galaxies at 2<z<3.5 show 2.79+/-0.31 ma g of surface brightness evolution relative to those at z<0.35, which i s significantly greater than the luminosity evolution over this redshi ft range. This can be explained by a size and luminosity evolution (SL E) model, in which the outer regions of spiral galaxies form later and with a longer time-scale than the centres, causing the half-light rad ius to increase with time. The blue-band luminosity density increases by a factor of similar to 2.5 from z similar to 0 to z similar to 2.85 , but falls back to approximately its zero-redshift value at z similar to 4. Galaxies at z similar to 4 appear to be similar in surface brig htness to those at z similar to 3, but smaller in size and lower in lu minosity. The angular size distributions of 22<I<26 galaxies in the Hu bble Deep Field, divided at z similar to 1.5 using UBI colours, sugges t that most size evolution occurs at z>1.5. A small sample of galaxies with I-K>3.8 (passively evolving galaxies at z>1) appeared to be no s maller than the PLE prediction, suggesting that it is primarily star-f orming galaxies that evolve in size.