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E. D. Reese, J. E. Carlstrom, J. J. Mohr, G. P. Holder (U.Chicago), M. K. Joy (NASA/MSFC), L. Grego (SAO), S. Patel (U.Alabama), W. L. Holzapfel (U.C.Berkeley)
With analysis of Sunyaev-Zel'dovich effect and x-ray data it is possible to determine the distances to galaxy clusters. Cosmic microwave background (CMB) photons inverse Compton scatter off of the hot intracluster medium (ICM) causing a small distortion in the CMB spectrum, the Sunyaev-Zel'dovich (SZ) effect. The SZ effect is proportional to the pressure integrated along the line of sight ~\int ne Te d\ell and appears as a small (~1~mK) decrement at centimeter wavelengths. The ICM also emits at x-ray wavelengths with a signal ~\int ne2 Te1/2 d\ell for bremsstrahlung radiation. Taking advantage of the different dependencies on the electron density, ne, one can solve for the size of the cluster. One then has a ruler with which to measure the angular diameter distance to the cluster, independently of the distance ladder.
We present our method and distances for a sample of our imaged SZ effect clusters. We use our interferometric cm-wave observations of the SZ effect at the BIMA and OVRO observatories and archival ROSAT x-ray data. We perform a maximum likelihood fit to the SZ and x-ray data simultaneously using an isothermal spherical \beta-model. These fits yield information about the shape and density of the ICM. We can then use these clusters to determine the Hubble constant. The largest source of observational uncertainty in H\circ, ~0%, is the x-ray determined electron temperature. Possible systematics are discussed, the largest being the assumption of isothermality for the ICM. The Chandra observatory will greatly reduce the uncertainty in Te and be able to detect temperature gradients as well as provide greater spatial resolution.
ER acknowledges support by NASA GSRP Grant NGT-50173.
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