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Session 21 - Galaxies and Clusters of Galaxies.
Oral session, Monday, June 10
Humanities 3650,

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

L. Grego (Cal Tech), J. Carlstrom (Univ. of Chicago), M. Joy (NASA/MSFC)

We present new images of the Sunyaev-Zel'dovich effect at 30 GHz towards several 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 (.1 to 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, T is the gas temperature, and L is the line of sight spatial dimension of the gas. Since the gas itself emits bremsstrahlung radiation with an x-ray surface brightness proportional to n_e^2 T^1/2\times L, 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 lead to the determination of cosmological parameters, including the Hubble constant. A sensitive, unbiased imaging survey of clusters at both radio and x-ray wavelengths is necessary to make reliable estimates of these parameters. Here we present new images for such a survey from data obtained using the Owens Valley Millimeter Array, outfitted with low noise HEMT amplifier receivers operating from 26 to 36 GHz. The first images obtained with this system are presented in Carlstrom, Joy, amp; Grego (1996).

Although the SZ effect is small even for rich clusters, 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. For example, we achieve sensitivities of 120 \muJy rms or better in a 1' beam, corresponding to 50\muK Rayleigh-Jeans brightness temperature. The brightest clusters observed were detectedwith signal to noise levels above 15. We will present the new images and discuss the results and their implications.

\centerline REFERENCES

Carlstrom, Joy, amp; Grego 1996, ApJ, 456, L75-L78

Program listing for Monday