X-MAS2: Study Systematics on the ICM Metallicity Measurements

X-ray measurements of the intracluster medium metallicity are becoming more and more frequent due to the availability of powerful X-ray telescopes with excellent spatial and spectral resolutions. The information that can be extracted from measurements of the α-elements, such as oxygen, magnesium, and silicon, with respect to the iron abundance is extremely important to a better understanding of stellar formation and its evolutionary history. In this paper we investigate possible source of bias or systematic effects connected to the plasma physics when recovering metal abundances from X-ray spectra. To do this, we analyze six simulated galaxy clusters processed through the new version of our X-Ray Map Simulator (X-MAS), which allows us to create mock XMM-Newton EPIC MOS1 and MOS2 observations. By comparing the spectroscopic results inferred from the X-ray spectra to the expected values directly obtained from the original simulation, we find that (1) the iron is recovered with high accuracy for both hot (T > 3 keV) and cold (T < 2 keV) systems; at intermediate temperatures, however, we find a systematic overestimate, which depends inversely on the number counts; (2) oxygen is well recovered in cold clusters, while in hot systems the X-ray measurement may overestimate the true value by a up to a factor of 2-3; (3) being a weak line, the measurement of magnesium is always difficult; despite this, for cold systems (i.e., with T < 2 keV) we do not find any systematic behavior, while for very hot systems (i.e., with T > 5 keV) the spectroscopic measurement may strongly overestimate the true value by up to a factor of 4; and (4) silicon is well recovered for all the clusters in our sample. We investigate in detail the nature of the systematic effects and biases found in performing XSPEC simulations. We conclude that they are mainly connected with the multitemperature nature of the projected observed spectra and to the intrinsic limitation of the XMM-Newton EPIC spectral resolution, which does not always allow disentangling the emission lines produced by different elements.