Proceedings of the Particle Physics and Early Universe Conference (PPEUC).
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4 Conclusions 

The basic result from Fig.2 is clear: if the two radio decrements are indeed due to the thermal SZ effect in two clusters, then the critical model is in very serious trouble. On the other hand, an open model is capable of explaining the objects. While our modelling has been rather simple in that we have used power-law power spectra and assumed that the cluster gas fraction is constant over mass and epoch (see, e.g. Colafrancesco et al. (1997) for more detailed treatment of cluster evolution), in the present circumstance any reasonable evolution in the gas mass fraction would lead to a decrease in the SZ flux density of objects with small mass and/or at large redshift; hence, it would only make things more difficult for the critical model.

What about other possible caveats? Besides the fact that we still await definite confirmation of the true nature of the radio decrements (e.g., detections at other frequencies), the most important thing to be wary of is the possible bias associated with the fact that the RT was pointed at a known double quasar, not an a priori blank field. This seems less likely to be true of the VLA detection, in as much as there was no previously known quasar pair in that field (although one was subsequently found). In any case, we should have a better idea in the near future from other experiments as the amount of sky covered by SZ searches appears to be rapidly increasing. The present discussion brings to light the importance of such SZ searches (we note in particular that a square-degree search with the BIMA telescope is now feasible [Holzapfel, private communication]). A satellite mission covering the full sky, such as the Planck Surveyor, will be the culmination of such efforts.

Finally, we remark that the possible existence of clusters at redshifts much greater than unity should not be seen as exotic; quite the contrary, in open models, they are expected. If they are indeed out there, they would not have been detectable up until now by either optical or X-ray observations. One would imagine that they would first be seen by SZ searches, and these are just now beginning to provide some very interesting and tantalizing hints.


PPEUC Proceedings
Fri Jul 25 11:32:28 BST 1997