The gas distribution in the high-redshift cluster MS 1054-0321

Abstract

We investigate the gas mass distribution in the high redshift cluster MS 1054-0321 using Chandra X-ray and OCRA SZ effect data. We use a superposition of offset $\beta$-type models to describe the composite structure of MS 1054-0321. We find gas mass fractions $f_{gas}^\rm{X\mbox{-}ray} = 0.087_{-0.001}^{+0.005}$ and $f_{gas}^\rm{SZ} = 0.094_{-0.001}^{+0.003}$ for the (main) eastern component of MS 1054-0321 using X-ray or SZ data, but $f_{gas}^\rm{X\mbox{-}ray} = 0.030 _{-0.014}^{+0.010}$ for the western component. The gas mass fraction for the eastern component is in agreement with some results reported in the literature, but inconsistent with the cosmic baryon fraction. The low gas mass fraction for the western component is likely to be a consequence of gas stripping during the ongoing merger. The gas mass fraction of the integrated system is $0.060_{-0.009}^{+0.004}$: we suggest that the missing baryons from the western component are present as hot diffuse gas which is poorly represented in existing X-ray images. The missing gas could appear in sensitive SZ maps.