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Centro de Astrofísica da Universidade do Porto

The Sunyaev-Zel'dovich effect and the value of Ω0

D. Barbosa, J.G. Bartlett, A. Blanchard, J. Oukbir

Abstract
We consider the Sunyaev-Zel'dovich (SZ) effect as a probe of Ω0: Using a self-consistent modeling of X-ray clusters, we examine the dependence of both the mean Compton y parameter and the SZ source counts on Ω0. These quantities increase with decreasing Ω0 due to the earlier epoch of structure formation in low-density cosmogonies; the results depend only on the quantity of gas heated to the virial temperature of collapsed objects and are independent of the spatial distribution of the gas in the potential wells. Specifically, we compare two models which reproduce the present-day abundance of clusters - a biased, critical universe and an unbiased, open model with Ω0=0.3. We find that the mean y parameter approaches the current FIRAS limit of y<2.5x10-5 for the open model, demonstrating the importance of improving this limit on spectral distortions, and that the SZ source counts and corresponding redshift distribution differ significantly between the two cosmogonies; millimeter surveys covering a large area should thus provide interesting constraints on the density parameter of the Universe and on the evolution of the heated gas fraction in virialized objects.

Astronomy and Astrophysics
Volume 314, Page 13
October 1996

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Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

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