Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological
constraints. This is of special interest in the light of the tension between the Planck results of the primary temperature anisotropies of the CMB and Sunyaev-Zeldovich plus X-ray cluster counts analyses. We quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, we assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM temperatures through spectral fitting in the same, mostly isothermal, regions and compare them. Our work is an extension to a previous one using X-ray clusters by the IACHEC. Performing spectral fitting in the full energy band we find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. We demonstrate that effects like multitemperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. We conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints.
Major astrophysical questions related to the formation and evolution of structures, and more specifically of galaxy groups and clusters, will still be open in the coming decade and beyond: what is the interplay of galaxy, supermassive black hole, and
intergalactic gas evolution in the most massive objects in the Universe - galaxy groups and clusters? What are the processes driving the evolution of chemical enrichment of the hot diffuse gas in large-scale structures? How and when did the first galaxy groups in the Universe, massive enough to bind more than 10^7 K gas, form? Focussing on the period when groups and clusters assembled (0.5<z<2.5), we show that, due to the continuum and line emission of this hot intergalactic gas at X-ray wavelengths, Athena+, combining high sensitivity with excellent spectral and spatial resolution, will deliver breakthrough observations in view of the aforementioned issues. Indeed, the physical and chemical properties of the hot intra-cluster gas, and their evolution across time, are a key to understand the co-evolution of galaxy and supermassive black hole within their environments.
Well-determined scaling relations between X-ray observables and cluster mass are essential for using large cluster samples for cosmology. Cluster relations such as the Lx-T, M-T, Lx-M relations, have been investigated extensively, however the questio
n remains whether these relations hold true also for groups. Some evidence supports a break at low masses, possibly caused by the influence of non-gravitational physics on low-mass systems. The main goal of this work is to test scaling relations for the low-mass range to check whether there is a systematic difference between clusters and groups, and to extend this method of reliable cluster mass determination for future samples down to the group regime. We compiled a statistically complete sample of 112 X-ray galaxy groups, 26 with Chandra data. Temperature, metallicity, and surface brightness profiles were created, and used to determine the main physical quantities and scaling relations. We then compared the group properties to the HIFLUGCS clusters and other samples. We present profiles and scaling relations of the whole sample. T and Z profiles behave universally, except for the cores. The Lx-T, M-T, Lx-M, Mg-M, M-Yx, and Lx-Yx relations are in good agreement with clusters. The Lx-T relation steepens for T<3keV, which could point to a larger impact of heating mechanisms on cooler systems. We found a strong drop in the gas mass fraction below 1keV, which indicates the ICM is less dominant in groups and the galaxies have a stronger influence on the system. In all relations the intrinsic scatter for groups is larger, which appears not correlated with merger activity but could be due to scatter caused by baryonic physics in the group cores. We also demonstrate the importance of selection effects. We have found evidence for a similarity break between groups and clusters. However this does not have a strong effect on scaling relations.
Context: Measurements of intracluster gas temperatures out to large radii are important for the use of clusters for precision cosmology and for studies of cluster physics. Previous attempts to measure robust temperatures at cluster virial radii faile
d. Aims: The goal of this work is to measure the temperature profile of the very relaxed galaxy cluster Abell 2204 out to large radii, possibly reaching the virial radius. Methods: Taking advantage of its low particle background due to its low-Earth orbit, Suzaku data are used to measure the outer temperature profile of Abell 2204. These data are combined with Chandra and XMM-Newton data of the same cluster in order to make the connection to the inner regions, unresolved by Suzaku, and to determine the smearing due to Suzakus PSF. Results: The temperature profile of Abell 2204 is determined from 10 kpc to 1800 kpc, close to an estimate of r200 (the approximation to the virial radius). The temperature rises steeply from below 4 keV in the very center up to more than 8 keV in the intermediate range and then decreases again to about 4 keV at the largest radii. Varying the measured particle background normalization artificially by +-10 percent does not change the results significantly. Predictions for outer temperature profiles based on hydrodynamic simulations show good agreement. In particular, we find the observed temperature profile to be slightly steeper but consistent with a drop of a factor of 0.6 from 0.3 r200 to r200, as predicted by simulations. Conclusions: Temperature measurements up to the virial radius seem feasible with Suzaku, when a careful analysis of the different background components and the effects of the PSF is performed. The result obtained here indicates that numerical simulations capture the intracluster gas physics well in cluster outskirts.
