Statistics of redshift periodicities

210 Current Issues in Cosmology
8
Count
6
4
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0
0 112.5 225 337.5 450 562.5 675
dV (km/sec)
Figure 17.2 Differential redshifts dV of 97 spiral galaxies in the Local Supercluster
with systemic redshifts measured to σ ≤ 3s −1 . Data are plotted in the frame of
reference V ⊙ = 216 km s −1 ,l ⊙ = 96 ◦ ,b ⊙ =−11 ◦ and smoothed with a cutoff
13 s −1 . The vertical lines are the best-fit periodicity of 37.5 s −1 . The first 21 cycles
are shown, but in fact the periodicity is detectable out to at least 90 cycles within
the LSC.
synthetic data sets and exploration of the power they generate by chance. The
hypothesis of non-periodicity is thereby rejected at a significance level ∼10 −5 .
In this case, since the galaxies are scattered over the sky, individual corrections
for the solar motion vary considerably and so the peak powers generated vary
strongly with the adopted solar apex. A real periodic signal occurring in the frame
of reference of a single velocity generates signals at other velocity vectors and
identifying the “real” signal is not a trivial exercise. To find the “true” solar vector,
the sensitivity of the signal to variations in the vector must be decreased. This can
be done in a number of ways, but the following approach is particularly instructive.
About half the galaxies in the sample belonged to small groups or associations
containing two to six companions. By looking for periodicity in the differential
redshifts within these groups, the sensitivity of the signal to V ⊙ may be decreased.
The resulting data set is small (50 galaxies) and so was enhanced by adding galaxies
obtained from a catalog by Tifft (1976) with measured signal-to-noise ratios greater
than 10 and which also belonged to cataloged groups. This enhanced data set
contained 80 galaxies in 28 groups scattered throughout the Local Supercluster.
The power distribution in these 28 LSC groups turns out to have a well-defined
maximum at ∼37.5kms −1 for a solar vector (remarkably!)
V ⊙ = 220 km s −1 , l ⊙ = 90.0 ◦ , b ⊙ = 0.0 ◦