C. The first generation of redshift surveys

1. CfA surveys

The first CfA redshift survey was undertaken by Huchra et al. (1983) who mapped some 2400 galaxies down to m 14.5 taken from the Zwicky catalog. This survey was too sparse to show definite structure.

The first survey to truly reflect the cosmic structure was the first CfA-II slice of de Lapparent et al. (1986), the "Slice of the Universe" (the smallest wedge in Fig. 6). The slice showed very clearly the "bubbly" nature of the large-scale structure, as the authors defined it. This important discovery generated a lot of publicity: cartoons appeared in newspapers depicting females with their arms in a sink full of soap bubbles, and the Encyclopaedia Britannica was updated to include a picture of the slice.

Prior to that there had been smaller surveys, such as the Perseus-Pisces region survey of Giovanelli and Haynes (1985) and the Coma-A1367 survey of Chincarini et al. (1983). These surveys had revealed rich structures in the distribution of galaxies, similar to Zel'dovich's predicted pancakes and voids. But since they were restricted to a volume around a major cluster of galaxies they could not be thought of as being representative of the universe as a whole.

At first glance it may seem that similar critique applies also to the CfA surveys, since the first CfA slice (de Lapparent et al., 1986) was indeed centered on the Coma cluster. However, the breadth of the slice (some 120 degrees on the sky) samples a far greater volume, and it was very deep for that time, extending to about 150h^-1Mpc. The slice also contains an unusual number of rich galaxy clusters. Subsequent surveys, the following CfA slices and the ESO Southern survey (da Costa et al., 1991) amply confirmed the impression given by the CfA slice.

The main source for redshifts during those years was 'Zcat', a heterogeneous compilation of galaxy redshifts by J. Huchra. But it took many years before the data from the CfA slices entered the public domain. This was unfortunate since many other groups would have liked to try their own analysis techniques on such a well defined sample. By the time that the data became available there existed already more substantial surveys with publicly available data and much of the impetus of the CfA slices, apart from the fine work done by the Harvard group itself, was lost.

The work to improve and extend the CfA surveys has continued. The Century Survey (Geller et al., 1997) covers the central 1° region of the famous CfA-II slice, but is much deeper, extending to R = 16.1 in the apparent magnitude and to 450h^-1Mpc in space. The final CfA catalog is the Updated Zwicky Catalog (Falco et al., 1999) that includes uniform measurements of almost all (about 19,000) galaxies of the Zwicky catalog (with the magnitude limit of m_Zw 15.5) in the northern sky. Nowadays catalogs are made public as soon as possible; the CfA redshift catalogs can be obtained from the web-page of the Smithsonian Astronomical Observatory Telescope Data Center (http://tdc-www.harvard.edu/).

2. SSRS and ORS

The Southern Sky Redshift Survey (da Costa et al., 1991) was meant to complement the original CfA survey, mapping galaxies in the southern sky. It includes almost 2000 redshifts; the followup survey, the extended SSRS (da Costa et al., 1998) with about 5400 redshifts mirrored the Second CfA survey for the southern sky. These catalogs were mostly used for comparison with the CfA survey results; they were made public at once and produced many useful results. Presently they are available from the Vizier database (http://vizier.u-strasbg.fr).

The Optical Redshift Survey (Santiago et al., 1995), had a depth of 80h^-1Mpc, similar to the first CfA survey, but attempted a complete coverage of the sky (except for the dusty avoidance zone around the galactic equator). They measured about 1300 new redshifts, including about 8500 redshifts in total. This survey was heavily exploited to describe the nearby density fields, to estimate the luminosity functions, galaxy correlations, velocity dispersions etc. The catalog and the publications can be found in http://www.astro.princeton.edu/~strauss/ors/.

3. Stromlo-APM and Durham/UKST redshift surveys

The Stromlo-APM redshift survey (Loveday et al., 1996) is a sparse survey (1 in 20) of some 1800 optically selected galaxies brighter than the apparent magnitude limit B 17 taken from the APM survey of the Southern sky. As the APM survey (Maddox et al., 1990) itself, the Stromlo-APM survey was an important data source and generated several important results on correlation functions in real and redshift space, power spectra, redshift distortions, cosmological parameters, bias and so on. It was eventually put into the public domain, although rather too late to be of much use to any third party investigators.

The APM survey was also used to generate a galaxy cluster catalog. The APM cluster redshift catalog (Dalton et al., 1997) was the first objectively defined cluster catalog. It not only provided important data on the distribution of clusters, it also provided an assessment of the reliability of the only cluster source available before that, the Abell cluster catalog.

The Durham/UKST redshift survey (Ratcliffe et al., 1998) measured redshifts for about 2500 galaxies around the South Galactic Pole. The depth of the survey was similar to that of the Stromlo-APM survey, and it was also a diluted survey sampling 1 galaxy in 3.

These catalogs can be found now at the Vizier site (see above).

4. IRAS redshift samples: PSCz

The story of the IRAS (Infrared Astronomical Satellite) redshift catalogs stresses the importance of having a good base photometric catalog before starting to measure redshifts. As galactic absorption in infrared is much smaller than in the optical bands, the IRAS Point Source Catalog (PSC) covers uniformly almost all of the sky. This catalog was used to select galaxies for redshift programs, which extended down to successively smaller flux limits: the 2 Jy survey of Strauss et al. (1992) with 2658 galaxies; the 1.2 Jy survey of Fisher et al. (1995) added 2663 galaxies; and the 0.6 Jy sparse-sampled (1 in 6) QDOT survey of Lawrence et al. (1999) with 2387 galaxies. This culminated in the PSCz survey of some 15000 galaxies by Saunders et al. (2000), which includes practically all IRAS galaxies within the 0.6 Jy flux limit.

The IRAS redshift catalogs have been used for the usual battery of large-scale studies, but their main advantage is their full-sky coverage (about 84%). This allows using the Wiener-type reconstruction methods to derive the true density and velocity fields, and to get an independent estimate of the biasing parameter. The first fields to be studied were taken from the 2 Jy survey by Yahil et al. (1991), the last fields came from the PSCz survey by Branchini et al. (1999) and Schmoldt et al. (1999).

The PSCz survey has also been used for fractal studies. Although the IRAS samples are not too deep (PSCz extends to about 200h^-1 Mpc), Pan and Coles (2000) found that multifractal analysis shows a definite crossover to homogeneity already before this scale.

5. ESO Deep Slice and the Las Campanas redshift survey

The ESO Deep Slice (Vettolani et al., 1998) measured redshifts of 3300 galaxies down to the blue magnitude b_J = 19.4 in the B_J, R, I photometric system (Gullixson et al., 1995). The surveyed region is a 1° × 22° strip of depth about 600 h^-1 Mpc. The most interesting discussion that this data caused was about the fractal nature of the large-scale galaxy distributions. While Scaramella et al. (1998) found the correlation dimension D = 3, Joyce et al. (1999) showed that a more reasonable choice of the K-correction (redshift-dependent apparent dimming of galaxies) gave a clearly fractal D = 2 correlation dimension.

The Las Campanas Redshift Survey (Shectman et al., 1996) had a similar geometry, six thin parallel slices (1.5° × 90°) with the depth about 750 h^-1Mpc (z 0.25). The survey team measured redshifts of about 24000 galaxies in these slices. This was the first deep survey of sufficient volume that it could be used to test if our knowledge of the nearby Universe was sufficient to describe more distant regions. The usual tests included the luminosity functions (these were found to depend on galaxy density and morphology), second- and third-order correlation functions, power spectra, and fractal properties. A catalog of groups of galaxies was generated. The survey results were quickly made public: the general interest in the data was high and close to a hundred papers have been published using these data.