Two new telescope/instrument combinations came on line in the mid 1990s that resulted in a dramatic increase in our ability to observe distant galaxies. The refurbishment mission that added the WFPC2 camera to HST, along with its corrective optics, plus the commissioning of the Low Resolution Imaging Spectrograph on the Keck I telescope provided new, and complementary, capabilities for observing faint, small, low surface brightness objects. This led to a remarkable resurgence of interest in distant galaxies, and a large increase in the statistical and quantitative veracity of the resulting data.
HST WFPC2 imaging has provided us opportunities to resolve distant galaxies, and extend our morphological and structural characterizations to galaxies at much higher redshift - the limitation now is largely one of S/N due to the effect of the cosmological (1 + z)4 surface brightness dimming and to the (often) large photometric K-corrections due to the rest frame shift into the UV. Some of the best examples of the imaging capabilities of HST have been seen in the multi-color images of the HDF and the ``Groth'' Survey strip in 1995, and the HDF-S in 1998, and in the deep images of many intermediate redshift (i.e., z ~ 0.2-1) clusters.
The multi-slit spectroscopy from Keck with the LRIS spectrograph has proven to be an ideal complement of the the HST imaging, allowing 30-40 galaxy redshifts to be measured at once to fainter than I ~ 25. With Keck plus LRIS it has become possible to routinely derive redshifts for objects several magnitudes fainter than was practical in major (and important) surveys carried out earlier this decade on 4-m class telescopes (e.g., the CFRS, Lilly et al. 1995).
The major developments of the last few years are:
(1.) - the measurement of large numbers of redshifts for z ~ 3-4 galaxies by Steidel and collaborators;
(2.) - the identification of several strongly-lensed (and hence highly-magnified) z ~ 2-5 galaxies;
(3.) - the detection of a number of z > 5 galaxies;
(4.) - the characterization of the star formation history of the universe by Madau and others (the ``Madau'' plot - SFR vs redshift);
(5.) - the recognition of the impact of dust on the UV fluxes from high redshift galaxies;
(6.) - the discovery of distant galaxies that are strong submm sources with the JCMT SCUBA submm detector.
(7.) - the utilization of increasingly more accurate photometric redshifts;
The improvements that are planned for HST imaging with the ACS (the new Advanced Camera), which will provide a gain of 10X in the area-throughput product (the figure-of-merit most appropriate for imaging surveys), and the dramatic increase in the numbers of 6.5-m to 10-m ground-based telescopes with their next generation optical and near-IR multi-object spectrographs will lead to an even greater rate of progress in the high redshift galaxy field within just a few years.