The technique for obtaining radial velocities of g ?Taxies from UK Schmidt
telescope objective -prism spectra, first developed by Cooke (1980), is
used here to investigate the possibility of using these radial velocities
to produce a large -scale survey of the Universe in three dimensions. A
4.8' x 5.2' region of the sky in ESO /SERC survey field 145 is examined,
which contains part of the Indus supercluster. Computer programs are
used to obtain a large sample of spectra from a measurement of the
plate of this region by the Edinburgh COSMOS machine in its mapping
mode. The Indus region surveyed is found to contain no obvious
large -scale features, but several small ones.
The reliability of objective -prism redshifts is tested by measuring
some of the areas a second time, and the objective -prism redshifts are
also calibrated by comparing them with redshifts obtained independently
from slit spectra. The effective "redshifts" of stellar spectra are
measured to check the zero point of the redshift scale. The results
indicate that the accuracy of the redshifts in the COSMOS sample is
not as good as expected, and that there is a systematic drift in
redshift zero point with magnitude. This situation may be improved by
using a magnitude- independent method of wavelength calibration and by
limiting the sample to images brighter than B - 18. It is found to be
difficult to determine redshifts reliably using only the one standard
feature used by Cooke (1980), and around 57. of the spectra this
feature is mis- identified, causing a redshift discrepancy of around +0.1.
A feature in some stellar spectra, at 4470A, causes them to appear like
galaxies on the objective -prism plate, and these are found to be
contaminating the sample, causing an excess of redshifts in the range
0.11 -0.13.
The objective -prism sample is paired with a sample of images
from the direct plate of the region which have been automatically
separated into stars and galaxies. It is found that redshifts are
attained for about 207. of galaxies, but that this fraction decreases
with magnitude. A large fraction of objects fainter than B - 18.5 are
found to be compact. Most of these are contaminating stars, but
there is marginal evidence for the existence of a small population of
compact galaxies in the rich clusters of the Indus supercluster
