Letter to the Editor

Calibration of the galaxy cluster M₅₀₀–Y relation with XMM-Newton

¹ Laboratoire AIM, DAPNIA/Service d'Astrophysique - CEA/DSM - CNRS - Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: Monique.Arnaud@cea.fr
² CESR, 9 Av. du colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
³ Max-Planck-Institut für extraterrestriche Physik, Giessenbachstraße, 85748 Garching, Germany

Received: 24 August 2007
Accepted: 9 September 2007

Abstract

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 10¹³–10¹⁵  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.