Astron. Astrophys. 336, 425-432 (1998)

7. Summary

In summary, we have seen the possible implications of the recently discovered radio decrements in the VLA and the Ryle Telescope. If the spectra of these two objects confirm an origin in the thermal SZ effect from two galaxy clusters, then a critical model would be in serious trouble. A large part of the importance of these two objects arises from the stringent X-ray and optical limits on the two fields. This argues that the supposed clusters are at very large redshift. This has been the key, because the SZ counts (the cluster abundance) at large redshift are enormously different between a critical and an open model. While such clusters are essentially non-existent at in a critical model, they are to be expected in open models, even at redshifts as large as 4.

However, all is not necessarily well with the open model in light of constraints on spectral distortions and temperature fluctuations of the cosmic microwave background. Barbosa et al. (1996) show that an open model with the power spectrum chosen here violates the FIRAS limit on y (assuming a constant ). We may also estimate the rms temperature fluctuations created by the unresolved cluster population by applying a P-D analysis (Condon 1974) to our cluster counts. We find that our fiducial open model here actually violates the present limit set by the SuZIE instrument (Church et al. 1997). The significance of these shortcomings should be addressed with more careful modeling of the counts and predicted fluctuations, and with a statistical comparison more appropriate to the non-Gaussian nature of the induced temperature fluctuations (Bartlett et al., in preparation).

Our modeling of the cluster population is consistent and phenomenological in that it uses the X-ray luminosity-temperature relation required to explain the observed redshift distribution of EMSS clusters (Oukbir & Blanchard 1997; Sadat et al. 1998) to find the expected X-ray flux and deduce the corresponding redshift limits. The discussion has focused on the comparison between a critical model and a fiducial open model. Such a simple comparison just to highlight the possible implications seems justified at this juncture due to the preliminary nature of the data, and the procedure demonstrates the value of cluster SZ searches. We await future results with anticipation, noting for now that it is already possible to perform an SZ survey of square degree (Holzapfel, private communication; Holzapfel et al. 1997).

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998
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