Annu. Rev. Astron. Astrophys. 1991. 29: 499-541 Copyright © 1991 by Annual Reviews. All rights reserved

3.3 3-D Surveys

Wide-angle surveys designed to sample a specific volume are the best for topological studies of the three-dimensional structure. Such surveys can have practical restrictions imposed by galactic extinction, sky coverage of the telescope used, and limits of the target catalog, usually in apparent magnitude, flux, or diameter, and may also be restricted by morphology or surface brightness constraints on detectability. Each survey must then be evaluated in light of the biases introduced by the selection process. Below, we discuss the major three-dimensional surveys.

THE LOCAL SUPERCLUSTER SURVEY With the goal of improving significantly our knowledge of the structure of the local universe, Fisher & Tully (1981) during the 1970s observed 1787 galaxies at 21 cm, using the 300-foot and 140-foot telescopes at Green Bank and the 100-meter telescope at Effelsberg. Their survey was constrained by loose criteria, biased by their aim to preferentially select nearby galaxies: to > - 45°, they selected large-angular-diameter objects of spiral or irregular morphology, which upon visual inspection on the Palomar Observatory and Whiteoak Extension Sky Surveys (POSS) appeared to be nearby. While this survey revealed in great detail the structure of the Local Supercluster, it is manifestly incomplete for early morphological types and for distances beyond 1000 km s^-1. However this survey, which contributed 1171 new redshifts, was the largest in scope at the time and marked the entrance of the 21-cm line as a main performer in the study of large-scale structure. Tully & Fisher (1987) more recently produced a detailed picture of the structure of the Local Supercluster, with the additional inclusion principally of earlytype galaxies of Sandage (1978).

THE CFA SURVEY The first ambitious survey of the past decade was that carried out by Davis et al (1982), known as the CfA survey. This effort aimed at completing (to a limit m_cgcg = 14.5) anorthern-hemisphere sample derived from the CGCG: The boundaries of the survey were 0°, b 40°, in the northern galactic gap, and - 2.5°, b - 30°, in the southern one. The CfA survey compilation (Huchra et al 1983) lists 2401 redshifts; nearly 60% of which were contributed by the CfA group using the 1.5-m Tillinghast reflector at Mt. Hopkins, an instrument since dedicated to the CfA redshift effort. The CfA survey has been used by many authors as the basis of statistical studies of the three-dimensional distribution of galaxies, the distribution and nature of galaxy groups, and the characteristics of galaxy segregation. Huchra (1988) has given a review of the CfA effort and the results derived from it.

THE PISCES-PERSEUS SURVEY The advent of low-noise receivers, coupled with the great collecting area of the Arecibo reflector and advances in spectrometer technology, made possible the pursuit of ambitious surveys with that instrument even within the open competition framework of a national center. Throughout the last decade, Giovanelli, Haynes, and collaborators (Giovanelli & Haynes 1985, Giovanelli et al 1986b, Haynes et al 1988, Giovanelli & Haynes 1989a, Wegner et al 1990b) carried out observations of a sample of approximately 5000 galaxies in the general region of the Pisces-Perseus supercluster, defined by b 10° and 0°. This sample includes all CGCG galaxies (to m = 15.7) and all those of UGC size 1' or greater within the sampled region. They inspected and classified non-UGC galaxies on the POSS, and observed at 21 cm (primarily at Arecibo and with the Green Bank 300-foot telescope outside of the Arecibo horizon) all galaxies of types S0a or later. Galaxies of earlier types of unknown redshift and spirals undetected at 21 cm were observed at the McGraw-Hill 2.4-m optical telescope. The overall sample is better than 85% complete; the weakest areas-with completion rates near 65% - correspond to the regions north of = + 35° and south of = 3°, reflecting zenithal limitations of the Arecibo antenna currently in the process of correction. This effort has contributed new redshifts for approximately 3500 galaxies. Giovanelli (1990) summarizes recent findings. Haynes & Giovanelli (1986, 1988) review analyses of the large-scale structural properties of this region. Topological details are described by Giovanelli et al (1986a), Gott et al (1989), and Ryden et al (1989). Void probability statistics are described by Fry et al (1989). Merighi et al (1986) survey neighboring areas, and Maurogordato et al (1990) map the extension of the supercluster towards southern declinations.

THE SOUTHERN SKY REDSHIFT SURVEY (SSRS) Until late in the 1980s, the redshift coverage of the southern hemisphere was quite uneven, in part because of fewer instrumental resources in the South and in part because a high-quality galaxy catalog was not available until Lauberts' (1982) ESO Uppsala Survey of the ESO (B) Atlas. Da Costa et al (1988) combined several efforts, including that of Menzies et al (1989), and produced a catalog of 2028 redshifts that cover 1.75 sr south of = - 17.5° and below b = - 30°. Because Lauberts' catalog was not photometrically complete, da Costa et al selected objects based on an angular size, given by log - D(0)_lim > 0.1, where D(0) is a diameter in arc minutes, corrected to face-on appearance. A conversion of this limit to one of apparent magnitude would depend upon morphological type, but on the average the depth of this sample is comparable to a blue m_lim 14.8. Da Costa et al (1989) have extended the SSRS effort to a second region of 135° x 10°, south of b = -30° and at -40° -30°. Converting Lauberts' diameters to a magnitude scale, they have surveyed galaxies earlier than Sbc to a blue magnitude limit of 15.1, and are currently reaching completion to 15.5 in that region. A detailed graphic analysis of the galaxian distribution in the southern galactic cap is given by Pellegrini et al (1990).

THE IRAS SURVEY The Infrared Astronomical Satellite (IRAS), which flew in 1983, produced a four-band all-sky catalog of sources. Yahil et al (1986) and Meiksin & Davis (1986) independently used positions and fluxes of galaxies in the catalog to show the existence of a dipole anisotropy in the far infrared source counts that points within about 30° of that measured for the cosmic microwave background. This result suggested that, over very large scales, the IRAS galaxies trace the mass that might be responsible for the Local Group's peculiar motion. Because IRAS fluxes are little affected by galactic extinction, a reliable nearly all-sky sample can be produced. Yahil (1988) reviews the extension of this effort, which involves the completion of the redshift data base for the galaxies in the IRAS sample. The overall sample, as discussed by Strauss et al (1990), includes 2649 galaxies and covers 87.6% of the sky; the redshift collection has been completed and partly published by Strauss & Huchra (1988), and Dey et al (1990). Parallel efforts along the same lines have been carried out by Lawrence et al (1986) and Leech et al (1988), who chose to concentrate their redshift survey of IRAS galaxies to high galactic latitudes.