Calibration of the galaxy cluster M500-Yx relation with XMM-Newton

Abstract

The quantity Yx, the product of the X-ray temperature T x and gas mass Mg, has recently been proposed as a robust low-scatter mass indicator for galaxy clusters. Using precise measurements from XMM-Newton data of a sample of 10 relaxed nearby clusters, spanning a Y x range of 1013-1015 M·keV, we investigate the M500-Yx relation. The M 500-Yx data exhibit a power law relation with slope a = 0.548 ± 0.027, close to the self-similar value (3/5) and independent of the mass range considered. However, the normalisation is ∼20% below the prediction from numerical simulations including cooling and galaxy feedback. We discuss two effects that could contribute to the normalisation offset: an underestimate of the true mass due to the hydrostatic equilibrium assumption used in X-ray mass estimates, and an underestimate of the hot gas mass fraction in the simulations. A comparison of the functional form and scatter of the relations between various observables and the mass suggest that Yx may indeed be a better mass proxy than Tx or Mg,500. © ESO 2007.