| 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 mcgcg = 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 mlim 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.