Context. The exploitation of clusters of galaxies as cosmological probes relies on accurate measurements of their total gravitating mass. X-ray observations provide a powerful means of probing the total mass distribution in galaxy clusters, but might be affected by observational biases and rely on simplistic assumptions originating from our limited understanding of the intracluster medium physics.Aims. This paper is aimed at elucidating the reliability of X-ray total mass estimates in clusters of galaxies by properly disentangling various biases of both observational and physical origin. Methods. We use N-body/SPH simulation of a large sample of ∼100 galaxy clusters and investigate total mass biases by comparing the mass reconstructed adopting an observational-like approach with the true mass in the simulations. X-ray surface brightness and temperature profiles extracted from the simulations are fitted with different models and adopting different radial fitting ranges in order to investigate modeling and extrapolation biases. Different theoretical definitions of gas temperature are used to investigate the effect of spectroscopic temperatures and a power ratio analysis of the surface brightness maps allows us to assess the dependence of the mass bias on cluster dynamical state. Moreover, we perform a study on the reliability of hydrostatic and hydrodynamical equilibrium mass estimates using the full three-dimensional information in the simulation. Results. A model with a low degree of sophistication such as the polytropic β-model can introduce, in comparison with a more adequate model, an additional mass underestimate of the order of ∼10% at r 500 and ∼15% at r 200 . Underestimates due to extrapolation alone are at most of the order of ∼10% on average, but can be as large as ∼50% for individual objects. Masses are on average biased lower for disturbed clusters than for relaxed ones and the scatter of the bias rapidly increases with increasingly disturbed dynamical state. The bias originating from spectroscopic temperatures alone is of the order of 10% at all radii for the whole numerical sample, but strongly depends on both dynamical state and cluster mass. From the full three dimensional information in the simulations we find that the hydrostatic equilibrium assumption yields masses underestimated by ∼10-15% and that masses computed by means of the hydrodynamical estimator are unbiased. Finally, we show that there is excellent agreement between our findings, results from similar analyses based on both Eulerian and Lagrangian simulations, and recent observational work based on the comparison between X-ray and gravitational lensing mass estimates.

We compare X-ray hydrostatic and weak-lensing mass estimates for a sample of 12 clusters that have been observed with both XMM-Newton and Subaru. At an over-density of ∆ = 500, we obtain 1 − M X /M WL = 0.01 ± 0.07 for the whole sample. We also divided the sample into undisturbed and disturbed sub-samples based on quantitative X-ray morphologies using asymmetry and fluctuation parameters, obtaining 1 − M X /M WL = 0.09 ± 0.06 and −0.06 ± 0.12 for the undisturbed and disturbed clusters, respectively. In addition to non-thermal pressure support, there may be a competing effect associated with adiabatic compression and/or shock heating which leads to overestimate of X-ray hydrostatic masses for disturbed clusters, for example, in the famous merging cluster A1914. Despite the modest statistical significance of the mass discrepancy, on average, in the undisturbed clusters, we detect a clear trend of improving agreement between M X and M WL as a function of increasing overdensity, M X /M WL = (0.908 ± 0.004) + (0.187 ± 0.010) · log 10 (∆/500). We also examine the gas mass fractions, f gas = M gas /M WL , finding that they are an increasing function of cluster radius, with no dependence on dynamical state, in agreement with predictions from numerical simulations. Overall, our results demonstrate that XMM-Newton and Subaru are a powerful combination for calibrating systematic uncertainties in cluster mass measurements.

Results from a large set of hydrodynamical smoothed particle hydrodynamics (SPH) simulations of galaxy clusters in a flat ΛCDM cosmology are used to investigate the metal enrichment and heating of the intracluster medium (ICM). The physical modelling of the gas includes radiative cooling, star formation, energy feedback and metal enrichment which follow from the explosions of supernovae of type II and Ia. The metallicity dependence of the cooling function is also taken into account. The gas is metal‐enriched from star particles according to the SPH prescriptions. The simulations have been performed to study the dependence of final metal abundances and heating of the ICM on the numerical resolution and the model parameters. For a fiducial set of model prescriptions the results indicate radial iron profiles in broad agreement with observations; global iron abundances are also consistent with data. It is found that the iron distribution in the intracluster medium is critically dependent on the shape of the metal deposition profile. At large radii the radial iron abundance profiles in the simulations are steeper than those in the data, suggesting a dynamical evolution of simulated clusters different from those observed. For low‐temperature clusters simulations yield iron abundances below the allowed observational range, unless a minimum diffusion length of metals in the ICM is introduced. The simulated emission‐weighted radial temperature profiles are in good agreement with data for cooling flow clusters, but at very small distances from the cluster centres (∼2 per cent of the virial radii) the temperatures are a factor of ∼2 higher than the measured spectral values. The luminosity–temperature relation is in excellent agreement with the data; cool clusters (TX∼ 1 keV) have a core excess entropy of ∼200 keV cm2 and their X‐ray properties are unaffected by the amount of feedback energy that has heated the ICM. The findings support the model proposed recently by Bryan, where the cluster X‐ray properties are determined by radiative cooling. The fraction of hot gas fg at the virial radius increases with TX, and the distribution obtained from the simulated cluster sample is consistent with the observational ranges.

We present the X-ray properties and scaling relations of a large sample of clusters extracted from the Marenostrum MUltidark SImulations of galaxy Clusters (MU-SIC) dataset. We focus on a sub-sample of 179 clusters at redshift z ∼ 0.11, with 3.2 × 10 14 h −1 M ⊙ < M vir < 2 × 10 15 h −1 M ⊙ , complete in mass. We employed the X-ray photon simulator PHOX to obtain synthetic Chandra observations and derive observable-like global properties of the intracluster medium (ICM), as X-ray temperature (T X ) and luminosity (L X ). T X is found to slightly under-estimate the true mass-weighted temperature, although tracing fairly well the cluster total mass. We also study the effects of T X on scaling relations with cluster intrinsic properties: total (M 500 and gas M g,500 mass; integrated Compton parameter (Y SZ ) of the Sunyaev-Zel'dovich (SZ) thermal effect; Y X = M g,500 T X . We confirm that Y X is a very good mass proxy, with a scatter on M 500 − Y X and Y SZ − Y X lower than 5%. The study of scaling relations among X-ray, intrinsic and SZ properties indicates that simulated MUSIC clusters reasonably resemble the self-similar prediction, especially for correlations involving T X . The observational approach also allows for a more direct comparison with real clusters, from which we find deviations mainly due to the physical description of the ICM, affecting T X and, particularly, L X .

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