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Session 115 - Galaxies and Clusters of Galaxies.
Oral session, Thursday, January 16
Frontenac Ballroom,

[115.05] The Sunyaev--Zel'dovich Effect Imaged in Galaxy Clusters

L. Grego (Caltech), J. Carlstrom (U. Chicago), M. Joy (NASA MSFC), W. Holzapfel (U. Chicago)

We report progress on an interferometric imaging survey of the Sunyaev-Zel'dovich effect towards distant galaxy clusters. The Sunyaev-Zel'dovich effect is a spectral distortion imprinted on the cosmic microwave background radiation (CMBR) by the inverse--Compton scattering of the low energy CMBR photons by hot (10^8 K) intracluster gas. This distortion is manifested as a small temperature decrement (\leq 1 mK) at radio frequencies. The SZ effect is proportional to the integral of the gas pressure along the line of sight (n_e T\times L), where n_e is the electron density, and T is the gas temperature. The gas itself emits bremsstrahlung radiation with an x-ray surface brightness proportional to n_e^2 T^1/2\times L. Therefore, in addition to providing valuable information on the physics of the cluster gas, analysis of the SZ effect in conjunction with x-ray data can yield an estimate of L, which can consequently be used to derive an independent estimate of the distance to the cluster. Measurement of the SZ effect can therefore constrain the values of cosmological parameters, including the Hubble constant. We are continuing work on a sensitive, unbiased imaging survey of clusters at radio frequencies to make a reliable estimate of H_o.

Here we present centimeter wavelength images from recent observations at both the OVRO and BIMA millimeter arrays. The first results were reported in Carlstrom et al. (1996). although the SZ effect is small, use of highly sensitive receivers and the interferometric method's natural suppression of many systematic errors have enabled us to make high quality images of the effect. We routinely achieve sensitivities of 25 \muK, and so are able to make maps with signal to noise ratio in excess of 50 \sigma. we have obtained high signal to noise images of 18 clusters with redshifts ranging from z = 0.15 to 0.83. We will present these and fits to isothermal \beta models for the cluster gas. These results and preliminary comparison to x-ray data will be discussed.

\centerline REFERENCES

Carlstrom, Joy, amp; Grego 1996, ApJ, 456, L75

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