arXiv subjects

D. Barbosa

Publications and source records attributed to D. Barbosa.

21 records · Page 2Linked to original sources

arXiv1997

Holes in the Microwave Sky

We discuss the implications of two possible, recent Sunyaev-Zel'dovich (SZ) detections for which no optical or X--ray counterparts have been found. This suggests that the objects reside at high redshift, which is difficult to reconcile with a critical cosmology. We develop this argument and find that an open model with $\Omo=0.2$ remains consistent with what we currently know about the two objects. The reasoning also demonstrates the utility of SZ cluster searches.

astro-ph↗

arXiv1995

The Sunyaev-Zel'dovich Effect and the Value of Omega

We consider the Sunyaev-Zel'dovich (SZ) effect as a probe of Omega_o: 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 Omega_o. These quantities increase with decreasing Omega_o 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 Omega_o=0.3. We find that the mean y parameter approaches the current FIRAS limit of y<2.5 10^{-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.

astro-ph↗

arXiv1995

The Physical State of the Intergalactic Medium or Can We Measure Y?

We present an argument for a {\it lower limit} to the Compton-$y$ parameter describing spectral distortions of the cosmic microwave background (CMB). The absence of a detectable Gunn-Peterson signal in the spectra of high redshift quasars demands a high ionization state of the intergalactic medium (IGM). Given an ionizing flux at the lower end of the range indicated by the proximity effect, an IGM representing a significant fraction of the nucleosynthesis-predicted baryon density must be heated by sources other than the photon flux to a temperature $\go {\rm few} \times 10^5\, K$. Such a gas at the redshift of the highest observed quasars, $z\sim 5$, will produce a $y\go 10^{-6}$. This lower limit on $y$ rises if the Universe is open, if there is a cosmological constant, or if one adopts an IGM with a density larger than the prediction of standard Big Bang nucleosynthesis.

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