THE PHYSICAL PARAMETERS OF THE EVOLVING POPULATION OF FAINT GALAXIES

The excess number of blue galaxies at faint magnitudes is a subject of much controversy. Recent Hubble Space Telescope results have revealed a plethora of galaxies with peculiar morphologies tentatively identif ied as the evolving population. We report the results of optical spect roscopy and near-infrared photometry of a sample of faint HST galaxies from the Medium Deep Survey to ascertain the physical properties of t he faint morphological populations. We find four principal results. Fi rst, the population of objects classified as 'peculiar' are intrinsica lly luminous in the optical (M-B similar to -19), Secondly these syste ms tend to be strong sources of [O II] line luminosity. Thirdly the op tical-infrared colours of the faint population (a) confirm the presenc e of a population of compact blue galaxies and (b) show the stellar po pulations of irregular/peculiar galaxies encompass a wide range in age . Finally a surface-brightness comparison with the local galaxy sample of Frei et al, shows that these objects are not of anomalously low su rface brightness, rather we find that all morphological classes have e volved to a higher surface brightness at higher redshifts (z > 0.3).