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M. E. Jones, R. Saunders, K. Grainge, W. F. Grainger, A. Maggi (Cavendish Lab., U. Cambridge, UK)
H0 is usually calculated from SZ and X-ray data using several simplifying assumptions, including that the cluster atmosphere is a single isothermal phase with density described by a King model, with no non-thermal contribution to the pressure. We have investigated the effect of these assumptions and find that, although individual cluster parameters such as temperature and central SZ decrement may be considerably in error, these errors tend to cancel in the derivation of the value of H0. For the quality of SZ and X-ray data currently available, these systematic modelling errors are dominated by the measurement errors in the SZ effect and the X-ray temperature. The error in H0 due to assumption that the line-of-sight depth of the cluster is equal to its size in the plane of the sky can be reduced below 5% by using a sample of only ten clusters, even under pessimistic asumptions about the true distribution of cluster ellipticities.
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