2007A&A...474L..37A

The quantity Y_X, the product of the X-ray temperature T_X and gas mass M_g, 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 10¹³-10¹⁵M_☉keV, we investigate the M₅₀₀-Y_X relation. The M₅₀₀-Y_X data exhibit a power law relation with slope α=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 Y_X may indeed be a better mass proxy than T_X or M_g,500.