It is clear from the above discussion that redshifts of distant clusters of galaxies can be obtained with relative ease, although a substantial amount of observing time is required. The results agree with those derived from slit spectra. In the case of Cl (0024+1654), the redshift derived here is substantially larger than that found by Baum (1962).
The observations discussed above were made under conditions of good seeing, 1" diameter star images, and with an aperture sufficiently large that the resulting energy distributions are accurate insofar as absolute flux is concerned. They can therefore be used to investigate evolutionary effects. As was the case for determining the redshift, the absolute spectral energy distribution of the total light from nearby ellipticals (Schild and Oke 1971) is used for reference; these are shown in Figures 1, 2, and 3. As noted by Schild and Oke (1971) and by Whitford (1971), this energy distribution differs substantially from that of the nuclei of giant elliptical galaxies and M31. A comparison with recent unpublished data obtained by the author on the energy distribution in the disk outside the nucleus of M31 shows almost as large a difference as for the nuclei. Insofar as color is concerned, the integrated light of giant ellipticals has almost the same energy distribution as the nucleus (innermost 10") of M32.
The most striking feature of
Figures 1 -
3 is the apparent complete absence of
evolutionary effects insofar as the overall energy distributions are
concerned. In the case of
the Hydra cluster, where most of the points have
standard deviations of only 0.02-0.05
mag, the energy distribution is virtually identical with that of the
integrated light of
nearby giant ellipticals. For the cluster (0024+1654) the accuracy is
much lower, but
again the overall energy distributions are the same. In the case of
3C 295, apart from
the effects of emission lines, the energy distribution again is not
significantly different
from that of the standard galaxy. The
3727 line of [O II] located at
5448
(Minkowski 1960)
falls just inside the band plotted at
log 
= 14.738. It
undoubtedly spills over
into the next band at log =
14.745. It can be argued that the energy distribution for
3C 295 may be affected by nonthermal continuum
radiation. The good fit of the H- and
K-line drop suggests that this is not important. Furthermore, nonthermal
sources in
galaxies are typically much bluer in color than the background galaxy
(Oke 1972); the
fact that the observed energy distribution continues to drop rapidly in
the ultraviolet,
down to 2800 Å, suggests that any nonthermal contribution is small, at
least above 2800 Å.
In the case of 3C 295, the light travel time for q0 ranging from 0 to +1 is 3.2 to 2.7 x 109 years if the Hubble constant H0 is 100 km s-1 Mpc-1, and twice this long if H0 = 50 km s-1 Mpc-1 (Sandage 1961). With these ages the absence of evolutionary effects in color is in sharp contrast to the predictions of Tinsley (1968) and Tinsley and Spinrad (1971). At z = 0.46, they predict changes in the B - V color, for instance, amounting to 0.1-0.2 mag compared with those for nearby galaxies. Part of the discrepancy occurs because they do not fit their indices to a suitable energy distribution for a nearby galaxy. The observed absence of evolutionary color effects could perhaps be explained by using an evolutionary theory in which star formation was terminated early in the life of the galaxy. The adopted luminosity function also is of considerable importance. Their remarks about the change in luminosity with age are still applicable, but the effects will be smaller than they predict since their forecasts reflect an increase in flux in the violet which is not observed.
A second approach to studying evolutionary effects is to look at the various line indices (Tinsley and Spinrad 1971). Unfortunately, these indices represent small flux differences and the accuracy of the present data is not sufficient to make such an investigation meaningful. Furthermore, the present measurements are not necessarily made with the most sensitive bandpasses.
The present observations of 3C 295 and Cl (0024+1654) provide for the first time ground-based observations at rest wavelengths from 3200 to 2350 Å. In the case of 3C 295, there is a suggestion that the spectral energy distribution may become moderately flat below 2800 Å. In view of the large errors in this spectral range, no more can be said. This result is at least qualitatively similar to the results for M31 and other galaxies obtained by Code (1969) from OAO-2.