The observational view of galaxy evolution since z ~ 1 has improved considerably over the last few years as a result of several independent redshift surveys containing several hundred galaxies in the 0 < z < 1.5 range. The galaxies in these samples are representative of the brighter galaxies in the HDF (e.g., IAB < 22.5) but are nevertheless playing a major role in the history of star-formation in the Universe.
There is general agreement that the ultraviolet luminosity density of the Universe increases as roughly (1 + z)3-4 due to the appearance at high redshifts of luminous blue galaxies with colors similar to those of present-day Irr galaxies and luminosities around present-day L*.
The population of large disk galaxies (i.e., those with
-1 >
3.2h-150 kpc) has changed
relatively little to z ~ 0.8. The size function of galactic disks
(the number per unit
comoving volume per interval in disk scale length) seen at 0.5 <
z < 1.0 is very similar
to that measured locally by
de Jong et al. (1996b).
On the other hand, the average
properties of these large disk galaxies show several indications of
modestly increased
star-formation activity: elevated surface brightness, bluer overall
colors, increased [O II]
3727 equivalent widths and later type morphologies. These are consistent
with an increase
in the average star formation rate by a factor of 3-4, in accord with
the history of the
Milky Way disk that has been inferred from analysis of the solar neighborhood.
To redshifts z ~ 0.8, the largest changes to the bivariate size-luminosity function are due to fairly small galaxies with half-light radii r0.5 < 5h-150 kpc and MAB(B) ~ -20.5. These generally have late type morphologies (i.e., irregular/peculiar). The nature of these galaxies is not well understood at this point, but they may simply be the small disk galaxies seen today at MAB(B) < -19.