IS MS 1054-03 an exceptional cluster?: A new investigation of ROSAT HRI X-ray data

We reanalyzed the ROSAT HRI observation of MS 1054-03, optimizing the channel HRI selection and including a new exposure of 68 ks. From a wavelet analysis of the HRI image we identify the main cluster component and find evidence for substructure in the west, which might be either a group of galaxies falling onto the cluster or a foreground source. Our one- and two-dimensional analysis of the data show that the cluster can be fitted well by a classical beta model centered only 20 away from the central cD galaxy. The core radius and beta values derived from the spherical model (beta = 0.96(-0.22)(+0.48)) and the elliptical model (beta = 0.73 +/- 0.18) are consistent. We derived the gas mass and total mass of the cluster from the beta -model fit and the previously published ASCA temperature (12.3(-2.2)(+/-3.1) keV). The gas mass fraction at the virial radius is f(gas) = (14[-3, + 2.5] +/- 3)% for Omega (0) = 1, where the errors in square brackets come from the uncertainty on the temperature, and the remaining errors from the HRI imaging data. The gas mass fraction computed for the best-fit ASCA temperature is significantly lower than found for nearby hot clusters, f(gas) = (20.1 + 1.6)%. This local value can be matched if the actual virial temperature of MS 1054-03 were close to the lower ASCA limit (similar to 10 keV), with an even lower value of 8 keV giving the best agreement. Such a bias between the virial and measured temperature could be due to the presence of shock waves in the intracluster medium, stemming from recent mergers. Another possibility, which reconciles a high temperature with the local gas mass fraction, is the existence of a nonzero cosmological constant.