Context. The hot plasma in a galaxy cluster is expected to be heated to high temperatures through shocks and adiabatic compression. The thermodynamical properties of the gas encode information on the ...processes leading to the thermalization of the gas in the cluster’s potential well and on non-gravitational processes such as gas cooling, AGN feedback, shocks, turbulence, bulk motions, cosmic rays and magnetic field. Aims. In this work we present the radial profiles of the thermodynamic properties of the intracluster medium (ICM) out to the virial radius for a sample of 12 galaxy clusters selected from the Planck all-sky survey. We determine the universal profiles of gas density, temperature, pressure, and entropy over more than two decades in radius, from 0.01R500 to 2R500. Methods. We exploited X-ray information from XMM-Newton and Sunyaev-Zel’dovich constraints from Planck to recover thermodynamic properties out to 2R500. We provide average functional forms for the radial dependence of the main quantities and quantify the slope and intrinsic scatter of the population as a function of radius. Results. We find that gas density and pressure profiles steepen steadily with radius, in excellent agreement with previous observational results. Entropy profiles beyond R500 closely follow the predictions for the gravitational collapse of structures. The scatter in all thermodynamical quantities reaches a minimum in the range 0.2 − 0.8R500 and increases outward. Somewhat surprisingly, we find that pressure is substantially more scattered than temperature and density. Conclusions. Our results indicate that once accreting substructures are properly excised, the properties of the ICM beyond the cooling region (R > 0.3R500) follow remarkably well the predictions of simple gravitational collapse and require few non-gravitational corrections.
Galaxy clusters are the endpoints of structure formation and are continuously growing through the merging and accretion of smaller structures. Numerical simulations predict that a fraction of their ...energy content is not yet thermalized, mainly in the form of kinetic motions (turbulence, bulk motions). Measuring the level of non-thermal pressure support is necessary to understand the processes leading to the virialization of the gas within the potential well of the main halo and to calibrate the biases in hydrostatic mass estimates. We present high-quality measurements of hydrostatic masses and intracluster gas fraction out to the virial radius for a sample of 13 nearby clusters with available XMM-Newton and Planck data. We compare our hydrostatic gas fractions with the expected universal gas fraction to constrain the level of non-thermal pressure support. We find that hydrostatic masses require little correction and infer a median non-thermal pressure fraction of ∼6% and ∼10% at R500 and R200, respectively. Our values are lower than the expectations of hydrodynamical simulations, possibly implying a faster thermalization of the gas. If instead we use the mass calibration adopted by the Planck team, we find that the gas fraction of massive local systems implies a mass bias 1 − b = 0.85 ± 0.05 for Sunyaev–Zeldovich-derived masses, with some evidence for a mass-dependent bias. Conversely, the high bias required to match Planck cosmic microwave background and cluster count cosmology is excluded by the data at high significance, unless the most massive halos are missing a substantial fraction of their baryons.
Aims. We present the reconstruction of hydrostatic mass profiles in 13 X-ray luminous galaxy clusters that have been mapped in their X-ray and Sunyaev–Zeldovich (SZ) signals out to R200 for the ...XMM-Newton Cluster Outskirts Project (X-COP). Methods. Using profiles of the gas temperature, density, and pressure that have been spatially resolved out to median values of 0.9R500, 1.8R500, and 2.3R500, respectively, we are able to recover the hydrostatic gravitating mass profile with several methods and using different mass models. Results. The hydrostatic masses are recovered with a relative (statistical) median error of 3% at R500 and 6% at R200. By using several different methods to solve the equation of the hydrostatic equilibrium, we evaluate some of the systematic uncertainties to be of the order of 5% at both R500 and R200. A Navarro-Frenk-White profile provides the best-fit in 9 cases out of 13; the remaining 4 cases do not show a statistically significant tension with it. The distribution of the mass concentration follows the correlations with the total mass predicted from numerical simulations with a scatter of 0.18 dex, with an intrinsic scatter on the hydrostatic masses of 0.15 dex. We compare them with the estimates of the total gravitational mass obtained through X-ray scaling relations applied to YX, gas fraction, and YSZ, and from weak lensing and galaxy dynamics techniques, and measure a substantial agreement with the results from scaling laws, from WL at both R500 and R200 (with differences below 15%), from cluster velocity dispersions. Instead, we find a significant tension with the caustic masses that tend to underestimate the hydrostatic masses by 40% at R200. We also compare these measurements with predictions from alternative models to the cold dark matter, like the emergent gravity and MOND scenarios, confirming that the latter underestimates hydrostatic masses by 40% at R1000, with a decreasing tension as the radius increases, and reaches ∼15% at R200, whereas the former reproduces M500 within 10%, but overestimates M200 by about 20%. Conclusions. The unprecedented accuracy of these hydrostatic mass profiles out to R200 allows us to assess the level of systematic errors in the hydrostatic mass reconstruction method, to evaluate the intrinsic scatter in the NFW c − M relation, and to robustly quantify differences among different mass models, different mass proxies, and different gravity scenarios.
Context. Galaxy clusters are continuously growing through the accretion of matter in their outskirts. This process induces inhomogeneities in the gas density distribution (clumping) that need to be ...taken into account to recover the physical properties of the intracluster medium (ICM) at large radii. Aims. We studied the thermodynamic properties in the outskirts (R > R500) of the massive galaxy cluster Abell 2142 by combining the Sunyaev Zel’dovich (SZ) effect with the X-ray signal. Methods. We combined the SZ pressure profile measured by Planck with the XMM-Newton gas density profile to recover radial profiles of temperature, entropy, and hydrostatic mass out to 2 × R500. We used a method that is insensitive to clumping to recover the gas density, and we compared the results with traditional X-ray measurement techniques. Results. When taking clumping into account, our joint X-SZ entropy profile is consistent with the predictions from pure gravitational collapse, whereas a significant entropy flattening is found when the effect of clumping is neglected. The hydrostatic mass profile recovered using joint X-SZ data agrees with that obtained from spectroscopic X-ray measurements and with mass reconstructions obtained through weak lensing and galaxy kinematics. Conclusions. We found that clumping can explain the entropy flattening observed by Suzaku in the outskirts of several clusters. When using a method that is insensitive to clumping for the reconstruction of the gas density, the thermodynamic properties of Abell 2142 are compatible with the assumption that the thermal gas pressure sustains gravity and that the entropy is injected at accretion shocks, with no need to evoke more exotic physics. Our results highlight the need for X-ray observations with sufficient spatial resolution, and large collecting area, to understand the processes at work in cluster outer regions.
Achieving a robust determination of the gas density profile in the outskirts of clusters is a crucial step for measuring their baryonic content and using them as cosmological probes. The difficulty ...in obtaining this measurement lies not only in the low surface brightness of the intracluster medium (ICM), but also in the inhomogeneities of the gas associated with clumps, asymmetries and accretion patterns. Using a set of hydrodynamical simulations of 62 galaxy clusters and groups we study these kinds of inhomogeneities, focusing on the ones on large scales, which, unlike clumps, are difficult to identify. For this purpose we introduce the concept of the residual clumpiness, Cℛ, which quantifies the large-scale inhomogeneity of the ICM. After showing that this quantity can be robustly defined for relaxed systems, we characterize how it varies with radius, and with the mass and dynamical state of the halo. Most importantly, we observe that it introduces an overestimate in the determination of the density profile from the X-ray emission, which translates into a systematic overestimate of 6 (12) per cent in the measurement of M
gas at R
200 for our relaxed (perturbed) cluster sample. At the same time, the increase of Cℛ with radius introduces a ∼2 per cent systematic underestimate in the measurement of the hydrostatic-equilibrium mass (M
he), which adds to the previous one, generating a systematic overestimate of ∼8.5 per cent in f
gas in our relaxed sample. Because the residual clumpiness of the ICM is not directly observable, we study its correlation with the azimuthal scatter in the X-ray surface brightness of the halo, a quantity that is well constrained by current measurements, and in the y-parameter profiles, which will be obtained in the forthcoming Sunyaev-Zeldovich (SZ) experiments. We find that their correlation is highly significant (r
S = 0.6-0.7), allowing us to define the azimuthal scatter measured in the X-ray surface brightness profile and in the y-parameter as robust proxies of Cℛ. After providing a function that connects the two quantities, we find that correcting the observed gas density profiles using the azimuthal scatter eliminates the bias in the measurement of M
gas for relaxed objects, which becomes 0 ± 2 per cent up to 2R
200, and reduces it by a factor of 3 for perturbed ones. This method also allows us to eliminate the systematics on the measurements of M
he and f
gas, although a significant halo-to-halo scatter remains.
Aims. We present our analysis of a local (z = 0.04−0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with ...numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We have exploited the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We stacked the density profiles to detect a signal beyond r200 and measured the typical density and scatter in cluster outskirts. We also computed the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compared our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond ~r500. Comparing our density profiles with simulations, we find that bibradiative runs predict density profiles that are too steep, whereas runs including additional physics and/or treating gas clumping agree better with the observed gas distribution. We report high-confidence detection of a systematic difference between cool-core and non cool-core clusters beyond ~0.3r200, which we explain by a different distribution of the gas in the two classes. Beyond ~r500, galaxy clusters deviate significantly from spherical symmetry, with only small differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the ENZO simulations. Conclusions. Comparing our results with numerical simulations, we find that bibradiative simulations fail to reproduce the gas distribution, even well outside cluster cores. Although their general behavior agrees more closely with the observations, simulations including cooling and star formation convert a large amount of gas into stars, which results in a low gas fraction with respect to the observations. Consequently, a detailed treatment of gas cooling, star formation, AGN feedback, and consideration of gas clumping is required to construct realistic models of the outer regions of clusters.
Gas clumping in galaxy clusters Eckert, D; Roncarelli, M; Ettori, S ...
Monthly notices of the Royal Astronomical Society,
03/2015, Letnik:
447, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The reconstruction of galaxy cluster's gas density profiles is usually performed by assuming spherical symmetry and averaging the observed X-ray emission in circular annuli. In the case of a very ...inhomogeneous and asymmetric gas distribution, this method has been shown to return biased results in numerical simulations because of the n... dependence of the X-ray emissivity. We propose a method to recover the true density profiles in the presence of inhomogeneities, based on the derivation of the azimuthal median of the surface brightness in concentric annuli. We demonstrate the performance of this method with numerical simulations, and apply it to a sample of 31 galaxy clusters in the redshift range 0.04-0.2 observed with ROSAT/Position Sensitive Proportional Counter (PSPC). The clumping factors recovered by comparing the mean and the median are mild and show a slight trend of increasing bias with radius. For R < R..., we measure a clumping factor ... <1.1 , which indicates that the thermodynamic properties and hydrostatic masses measured in this radial range are only mildly affected by this effect. Comparing our results with three sets of hydrodynamical numerical simulations, we found that non-radiative simulations significantly overestimate the level of inhomogeneities in the intracluster medium, while the runs including cooling, star formation, and AGN feedback reproduce the observed trends closely. Our results indicate that most of the accretion of X-ray-emitting gas is taking place in the diffuse, large-scale accretion patterns rather than in compact structures. (ProQuest: ... denotes formulae/symbols omitted.)
Answers to the metal production of the Universe can be found in galaxy clusters, notably within their intra-cluster medium (ICM). The X-ray Integral Field Unit (X-IFU) on board the next-generation ...European X-ray observatory Athena (2030s) will provide the necessary leap forward in spatially-resolved spectroscopy required to disentangle the intricate mechanisms responsible for this chemical enrichment. In this paper, we investigate the future capabilities of the X-IFU in probing the hot gas within galaxy clusters. From a test sample of four clusters extracted from cosmological hydrodynamical simulations, we present comprehensive synthetic observations of these clusters at different redshifts (up to z ≤ 2) and within the scaled radius R500 performed using the instrument simulator SIXTE. Through 100 ks exposures, we demonstrate that the X-IFU will provide spatially resolved mapping of the ICM physical properties with little to no biases (⪅5%) and well within statistical uncertainties. The detailed study of abundance profiles and abundance ratios within R500 also highlights the power of the X-IFU in providing constraints on the various enrichment models. From synthetic observations out to z = 2, we have also quantified its ability to track the chemical elements across cosmic time with excellent accuracy, and thereby to investigate the evolution of metal production mechanisms as well as the link to the stellar initial mass-function. Our study demonstrates the unprecedented capabilities of the X-IFU of unveiling the properties of the ICM but also stresses the data analysis challenges faced by future high-resolution X-ray missions such as Athena.
Aims.
We present a cosmological analysis of abundances and stacked weak lensing profiles of galaxy clusters, exploiting the AMICO KiDS-DR3 catalogue. The sample consists of 3652 galaxy clusters with ...intrinsic richness
λ
*
≥ 20, over an effective area of 377 deg
2
, in the redshift range
z
∈ 0.1, 0.6.
Methods.
We quantified the purity and completeness of the sample through simulations. The statistical analysis has been performed by simultaneously modelling the co-moving number density of galaxy clusters and the scaling relation between the intrinsic richnesses and the cluster masses, assessed through stacked weak lensing profile modelling. The fluctuations of the matter background density, caused by super-survey modes, have been taken into account in the likelihood. Assuming a flat Λ cold dark matter (ΛCDM) model, we constrained Ω
m
,
σ
8
,
S
8
≡
σ
8
(Ω
m
/0.3)
0.5
, and the parameters of the mass-richness scaling relation.
Results.
We obtained Ω
m
= 0.24
−0.04
+0.03
,
σ
8
= 0.86
−0.07
+0.07
, and
S
8
= 0.78
−0.04
+0.04
. The constraint on
S
8
is consistent within 1
σ
with the results from WMAP and Planck. Furthermore, we got constraints on the cluster mass scaling relation in agreement with those obtained from a previous weak lensing only analysis.
ABSTRACT
The key to understand the nature of dark energy lies in our ability to probe the distant Universe. In this framework, the recent detection of the kinematic Sunyaev–Zel’dovich (kSZ) effect ...signature in the cosmic microwave background obtained with the South Pole Telescope (SPT) is extremely useful since this observable is sensitive to the high-redshift diffuse plasma. We analyse a set of cosmological hydrodynamical simulation with four different realizations of a Hu & Sawicki f(R) gravity model, parametrized by the values of $\overline{f}_{\rm R,0}$= (0, −10−6, −10−5, −10−4), to compute the properties of the kSZ effect due to the ionized Universe and how they depend on $\overline{f}_{\rm R,0}$ and on the redshift of reionization, zre. In the standard General Relativity limit ($\overline{f}_{\rm R,0}$= 0) we obtain an amplitude of the kSZ power spectrum of $\mathcal {D}^{\rm kSZ}_{3000}$$= 4.1\,$$\mu$K2 (zre= 8.8), close to the +1σ limit of the $\mathcal {D}^{\rm kSZ}_{3000}$$= (2.9\pm 1.3)\,$$\mu$K2 measurement by SPT. This corresponds to an upper limit on the kSZ contribute from patchy reionization of $\mathcal {D}^{\rm kSZ,patchy}_{3000}$$\lt 0.9\,$$\mu$K2 (95 per cent confidence level). Modified gravity boosts the kSZ signal by about 3, 12, and 50 per cent for $\overline{f}_{\rm R,0}$=(− 10−6, −10−5, −10−4), respectively, with almost no dependence on the angular scale. This means that with modified gravity the limits on patchy reionization shrink significantly: for $\overline{f}_{\rm R,0}$=−10−5 we obtain $\mathcal {D}^{\rm kSZ,patchy}_{3000}$$\lt 0.4\,$$\mu$K2. Finally, we provide an analytical formula for the scaling of the kSZ power spectrum with zre and $\overline{f}_{\rm R,0}$ at different multipoles: at ℓ = 3000 we obtain $\mathcal {D}^{\rm kSZ}_{3000}$ ∝ zre$^{0.24}\left(1+\sqrt{\left|\overline{f}_{\rm R,0}\right|}\right)^{41}$.
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