Context. Upcoming X-ray surveys like eROSITA require precise calibration between X-ray observables and mass down to the lowmass regime to set tight constraints on the fundamental cosmological parameters. Since an individual mass measurement is only possible for relatively few objects, it is crucial to have reliable and clearly understood scaling relations that relate the total mass to easily observable quantities. Aims. The main goal of this work is to constrain the galaxy group scaling relations corrected for selection effects, and to quantify the influence of non-gravitational physics at the low-mass regime. Methods. We analyzed XMM-Newton observations for a complete sample of galaxy groups selected from the ROSAT All-Sky Survey and compared the derived scaling properties with a galaxy cluster sample. To investigate the role played by the different non-gravitational processes we then compared the observational data with the predictions of hydrodynamical simulations. Results. After applying the correction for selection effects (e.g., Malmquist bias), the L X -M relation is steeper than the observed one. Its slope (1.66 ± 0.22) is also steeper than the value obtained by using the more massive systems of the HIFLUGCS sample. This behavior can be explained by a gradual change of the true L X -M relation, which should be taken into account when converting the observational parameters into masses. The other observed scaling relations (not corrected for selection biases) do not show any break, although the comparison with the simulations suggests that feedback processes play an important role in the formation and evolution of galaxy groups. Thanks to our master sample of 82 objects spanning two order of magnitude in mass, we tightly constrain the dependence of the gas mass fraction on the total mass, finding a difference of almost a factor of two between groups and clusters. We also found that the use of different AtomDB versions in the calculation of the group properties (e.g., temperature and density) yields a gas fraction of up to 20% lower than an older version.

Context. Robust X-ray temperature measurements of the intracluster medium (ICM) of galaxy clusters require an accurate energydependent effective area calibration. Since the hot gas X-ray emission of galaxy clusters does not vary on relevant timescales, they are excellent cross-calibration targets. Moreover, cosmological constraints from clusters rely on accurate gravitational mass estimates, which in X-rays 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 light of the tension between the Planck results of the primary temperature anisotropies of the cosmic microwave background (CMB) and Sunyaev-Zel'dovich-plus-X-ray cluster-count analyses. Aims. 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. Methods. 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 the different instruments. We use the stacked residual ratio method to evaluate the cross-calibration uncertainties between the instruments as a function of energy. Our work is an extension to a previous one using X-ray clusters by the International Astronomical Consortium for High Energy Calibration (IACHEC) and is carried out in the context of IACHEC. Results. Performing spectral fitting in the full energy band, (0.7-7) keV, as is typical of the analysis of cluster spectra, we find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. This confirms the previous IACHEC results obtained with older calibrations with high precision. The difference increases with temperature, and we quantify this dependence with a fitting formula. For instance, at a cluster temperature of 10 keV, EPIC temperatures are on average 23% lower than ACIS temperatures. We also find systematic differences between the three XMM-Newton/EPIC instruments, with the PN detector typically estimating the lowest temperatures. Testing the cross-calibration of the energy-dependence of the effective areas in the soft and hard energy bands, (0.7-2) keV and (2-7) keV, respectively, we confirm the previously indicated relatively good agreement between all instruments in the hard and the systematic differences in the soft band. We provide scaling relations to convert between the different instruments based on the effective area, gas temperature, and hydrostatic mass. 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...

The isotropy of the late Universe and consequently of the X-ray galaxy cluster scaling relations is an assumption greatly used in astronomy. However, within the last decade, many studies have reported deviations from isotropy when using various cosmological probes; a definitive conclusion has yet to be made. New, effective and independent methods to robustly test the cosmic isotropy are of crucial importance. In this work, we use such a method. Specifically, we investigate the directional behavior of the X-ray luminositytemperature (L X − T ) relation of galaxy clusters. A tight correlation is known to exist between the luminosity and temperature of the X-ray-emitting intracluster medium of galaxy clusters. While the measured luminosity depends on the underlying cosmology through the luminosity distance D L , the temperature can be determined without any cosmological assumptions. By exploiting this property and the homogeneous sky coverage of X-ray galaxy cluster samples, one can effectively test the isotropy of cosmological parameters over the full extragalactic sky, which is perfectly mirrored in the behavior of the normalization A of the L X − T relation. To do so, we used 313 homogeneously selected X-ray galaxy clusters from the Meta-Catalogue of X-ray detected Clusters of galaxies (MCXC). We thoroughly performed additional cleaning in the measured parameters and obtain core-excised temperature measurements for all of the 313 clusters. The behavior of the L X − T relation heavily depends on the direction of the sky, which is consistent with previous studies. Strong anisotropies are detected at a 4σ confidence level toward the Galactic coordinates (l, b) ∼ (280 • , −20 • ), which is roughly consistent with the results of other probes, such as Supernovae Ia. Several effects that could potentially explain these strong anisotropies were examined. Such effects are, for example, the X-ray absorption treatment, the effect of galaxy groups and low redshift clusters, core metallicities, and apparent correlations with other cluster properties, but none is able to explain the obtained results. Analyzing 10 5 bootstrap realizations confirms the large statistical significance of the anisotropic behavior of this sky region. Interestingly, the two cluster samples previously used in the literature for this test appear to have a similar behavior throughout the sky, while being fully independent of each other and of our sample. Combining all three samples results in 842 different galaxy clusters with luminosity and temperature measurements. Performing a joint analysis, the final anisotropy is further intensified (∼ 5σ), toward (l, b) ∼ (303 • , −27 • ), which is in very good agreement with other cosmological probes. The maximum variation of D L seems to be ∼ 16 ± 3% for different regions in the sky. This result demonstrates that X-ray studies that assume perfect isotropy in the properties of galaxy clusters and their scaling relations can produce strongly biased results whether the underlying reason is cosmological or related ...

We report the scaling relations derived by fitting the X-ray parameters determined from analyzing the XMM-Newton observations of 120 galaxy clusters in the Planck Early Sunyaev-Zel'dovich sample spanning the redshift range of 0.0593σ) of the M tot -T relation, pointing to an increase of the kinetic-to-thermal energy ratio with redshift. This is consistent with a scenario in which higher redshift clusters are on average more disturbed than their lower redshift counterparts.

The hypothesis that the late Universe is isotropic and homogeneous is adopted by most cosmological studies, including studies of galaxy clusters. The cosmic expansion rate H0 is thought to be spatially constant, while bulk flows are often presumed to be negligible compared to the Hubble expansion, even at local scales. The effects of bulk flows on the redshift–distance conversion are hence usually ignored. Any deviation from this consensus can strongly bias the results of such studies, and thus the importance of testing these assumptions cannot be understated. Scaling relations of galaxy clusters can be effectively used for this testing. In previous works, we observed strong anisotropies in cluster scaling relations, whose origins remain ambiguous. By measuring many different cluster properties, several scaling relations with different sensitivities can be built. Nearly independent tests of cosmic isotropy and large bulk flows are then feasible. In this work, we make use of up to 570 clusters with measured properties at X-ray, microwave, and infrared wavelengths to construct ten different cluster scaling relations and test the isotropy of the local Universe; to our knowedge, we present five of these scaling relations for the first time. Through rigorous and robust tests, we ensure that our analysis is not prone to generally known systematic biases and X-ray absorption issues. By combining all available information, we detect an apparent 9% spatial variation in the local H0 between (l, b)∼(280°−35°+35°, −15°−20°+20°) and the rest of the sky. The observed anisotropy has a nearly dipole form. Using isotropic Monte Carlo simulations, we assess the statistical significance of the anisotropy to be > 5σ. This result could also be attributed to a ∼900 km s−1 bulk flow, which seems to extend out to at least ∼500 Mpc. These two effects will be indistinguishable until more high-z clusters are observed by future all-sky surveys such as eROSITA.