|Annu. Rev. Astron. Astrophys. 1991. 29:
Copyright © 1991 by Annual Reviews Inc. All rights reserved
Redshift surveys are designed primarily to uncover the detailed three-dimensional structure in the galaxy distribution, to study the dynamics of galaxy aggregates, and ultimately to trace the past history of the development of such structure from primordial perturbations. As evidenced in Figure 2, the gross overall characteristics of the nearby universe are beginning to emerge. The distribution of galaxies is far from homogeneous; galaxies cluster on small scales, and, with less accurate measures, on larger scales as well. The progress made in the past quarter century in delineating the large-scale structure can be impressively realized by a quick review of past Annual Review articles on related subjects. In his 1965 article on the Clustering of Galaxies, Abell (1965) used the term ``second-order cluster'' in place of the now familiar ``supercluster''. While it was still controversial at that time, the concept of large-scale clustering has been proved through the acquisition of numerous redshifts. By 1983, Oort (1983) was able to describe the gross characteristics of the nearby superclusters (Coma, Perseus, Hercules, and the Local Supercluster, as well as other suspected ones), to note the equal importance of voids, and to hypothesize the existence of even larger structure on scales ~ 100 h-1 Mpc. In the same volume, Davis & Peebles (1983) discussed evidence for peculiar motions. In the 1970s, survey work painstakingly led to the acceptance of superclustering - the detail of the structure, rather than merely its existence, had started to emerge. The successful efforts of the 1980s have themselves driven the technological advances, particularly in the development of multiobject spectroscopy, that in turn promise more than one order of magnitude growth in the 1990s. Deep, sky-wide, photometric catalogs will complement the redshift efforts.
The next generation of redshift surveys, including those already underway, should give us the needed insight into the three-dimensional structure, allowing us to confidently refer to a fair sample. The increase in sample size will, in turn, provide more significance to statistical tests used to quantify the large-scale structure, to characterize its topology and scales, and to delineate and ultimately catalog both high density regions and voids. Deep surveys will allow the study of the correlation function on large scales: Does (r) go negative at ~ 20 h-1 Mpc or beyond? Many other questions remain. Is the universe a multifractal? Is there structure on scales larger than ~ 100 h-1 Mpc, and, especially, is there a preferred scale for the largest structures? The mapping of the deviations from Hubble flow will lead to the derivation of the mass distribution contributed by both luminous and dark matter. What is the relationship of galaxies and clusters to the underlying large-scale mass distribution in which they are embedded?
Studies of objects at high redshift will allow us to trace the time evolution of galaxy populations in luminosity, color, and with local density, and to follow the development of large-scale structure and substructure. Ultimately, we should pinpoint the epoch of onset of galaxy formation and may gain understanding of the processes responsible for producing the variety of structures we recognize today. All of this must in the end be reconciled with observations of the cosmic microwave background radiation, itself a target for surveys driven by new technologies for both ground- and space-based research.