|Annu. Rev. Astron. Astrophys. 1991. 29:
Copyright © 1991 by Annual Reviews Inc. All rights reserved
The desire to map the universe in three dimensions has provided the main stimulus for the growth of one of the most successful industries in the history of modern astronomy: the surveying of galaxy redshifts. After the pioneering work of Slipher, Humason, Mayall, and others in the earlier half of the century, the completion of the redshift data base for the Shapley-Ames Catalog by Humason et al (1956) and Sandage (1978) yielded the first accurate views of the local universe. In the last fifteen years, advances in detector and spectrometer technology at both optical and radio wavelengths have spurred a tremendous explosion in the galaxy redshift tally. The resulting view of the universe has proved both complex and complicated, and has fostered considerable effort to explain both the topology of the large-scale structure and its origin.
The growth of the redshift industry has paralleled other advances in astronomy, particularly in the past quarter century. The First Reference Catalogue of Bright Galaxies (de Vaucouleurs 1964) included about 1000 redshifts. its successor, the Second Reference Catalogue of Bright Galaxies (de Vaucouleurs et al 1976), contained four times as many. The compilation of 8250 (counting multiple entries for single objects) radial velocities by Palumbo et al (1983) presents, as closely as possible, a complete summary of observational efforts published before 1980.
While the majority of redshifts are obtained via optical spectroscopy, a significant contribution derives from the 21-cm H I line surveys of spirals and gas-rich dwarfs. Surveys conducted in the 21-cm line arrived relatively late as partners in the redshift industry, but improvements in receiver and spectrometer technology eventually led to the participation of radio astronomers. In the early 1970s, only 150 or so galaxies had a measured 21-cm redshift (Roberts 1975). Since then, radio astronomers have rapidly increased their productivity. Of the 30,000 or so galaxies with a measured redshift at the beginning of this decade, those that have been observed at 21 -cm account for over 12,000.
By any standards of human activity, the redshift industry is among the most successful, as it can boast a sustained growth rate in excess of 10% per year over its whole 80-year history, and has the potential to maintain its growth for the foreseeable future. Those engaged in this production effort never seem to have enough time left to reflect on achievements, and, more to the point, have little hope of their work having lasting value in review efforts such as this.
With this in mind, we attempt here to give a progress report on the recent advances in terms of the scientific results, technological advances and the sheer quantity of measurements in the midst of extraordinary growth. In order to cover the wide variety of cosmological problems explored by redshift surveys, we focus on the current horizons, on the comparison of strategies, and on the future promises of technological developments. Only cursory treatment is given to spectral characteristics other than the redshift, and we avoid reviewing quasar studies that lend themselves to a separate review. We have also focused on work of the 1980s rather than providing a complete historical development. Other recent reviews of redshift surveys have been written by Huchra (1988) and Geller & Huchra (1988), while Oort (1983) has summarized earlier results on large-scale structure.