Galaxy cluster analyses based on high-resolution observations of the Sunyaev-Zeldovich (SZ) effect have become common in the last decade. We present PreProFit, the first publicly available code designed to fit the pressure profile of galaxy clusters from SZ data. PreProFit is based on a Bayesian forward-modelling approach, allows the analysis of data coming from different sources, adopts a flexible parametrization for the pressure profile, and fits the model to the data accounting for Abel integral, beam smearing, and transfer function filtering. PreProFit is computationally efficient, is extensively documented, has been released as an open source Python project, and was developed to be part of a joint analysis of X-ray and SZ data on galaxy clusters. PreProFit returns χ 2 , model parameters and uncertainties, marginal and joint probability contours, diagnostic plots, and surface brightness radial profiles. PreProFit also allows the use of analytic approximations for the beam and transfer functions useful for feasibility studies.
We present resolved thermodynamic profiles out to 500 kpc, about r500, of the z = 1.75 galaxy cluster IDCS J1426.5+3508 with 40 kpc resolution. Thanks to the combination of Sunyaev–Zel’dovich and X-ray data sets, IDCS J1426.5+3508 becomes the most distant cluster with resolved thermodynamic profiles. These are derived assuming a non-parametric pressure profile and a very flexible model for the electron density profile. The shape of the pressure profile is flatter than the universal pressure profile. The IDCS J1426.5+3508 temperature profile is increasing radially out to 500 kpc. To identify the possible future evolution of IDCS J1426.5+3508 , we compared it with its local descendants that numerical simulations show to be 0.65 ± 0.12 dex more massive. We found no evolution at 30 kpc, indicating a fine tuning between cooling and heating at small radii. At 30 < r < 300 kpc, our observations show that entropy and heat must be deposited with little net gas transfer, while at 500 kpc the gas need to be replaced by a large amount of cold, lower entropy gas, consistent with theoretical expectation of a filamentary gas stream, which brings low entropy gas to 500 kpc and energy at even smaller radii. At r ≳ 400 kpc the polytropic index takes a low value, which indicates the presence of a large amount of non-thermal pressure. Our work also introduces a new definition of the evolutionary rate that uses unscaled radii, unscaled thermodynamic quantities, and different masses at different redshifts to compare ancestors and descendants. It has the advantage of separating cluster evolution, dependence on mass, pseudo-evolution, and returns a number with unique interpretation, unlike other definitions used in literature.
Entropy is an advantageous diagnostics to study the thermodynamic history of the intracluster plasma of galaxy clusters. We present the entropy profile of the Abell 2244 galaxy cluster derived both exclusively using X-ray data from the low-background Swift XRT telescope and also using Planck y data. The entropy profile derivation using X-rays only is robust at least to the virial radius because the cluster brightness is large compared to the X-ray background at low energies, temperature is strongly bounded by the lack of cluster X-ray photons at energies kT > 3 keV, and the XRT background is low, stable and understood. In the observed solid angle, about one quadrant, the entropy radial profile deviates from a power-law at the virial radius, mainly because of a sharp drop of the cluster temperature. This bending of the entropy profile is confirmed when X-ray spectral information is replaced by the Compton map. Clumping and non-thermal pressure support are insufficient to restore a power law entropy profile because they are bound to be small by: a) the agreement between mass estimates from different tracers (gas and galaxies), b) the agreement between entropy profile determinations based on combinations of observables with different sensitivities and systematics, and c) the low value of clumping as estimated using the azimuthal scatter and the gas fraction. Based on numerical simulations, ion-electron equilibration is also insufficient to restore a linear entropy profile. Therefore, the bending of the entropy profiles seems to be robustly derived and witnesses the teoretically-predicted decrease in the inflow through the virial boundary.
The thermal Sunyaev-Zeldovich (SZ) effect and the X-ray emission offer separate and highly complementary probes of the thermodynamics of the intracluster medium, particularly on their radial dependence. We already released JoXSZ, the first publicly available code designed to jointly fit SZ and X-ray data coming from various instruments to derive the thermodynamic radial profiles of galaxy clusters, including mass. JoXSZ follows a fully Bayesian forward-modelling approach, adopts flexible parametrization for the thermodynamic profiles and includes many useful options that users can customize according to their needs. We are including shear measurement in our joint analysis, and moving from single-cluster to multi-cluster analyses, allowing to quantify the heterogeneity of thermodynamic properties within the cluster population. At the same time, we are creating a suitable framework that effciently stores and optimally processes huge volumes of data being released by the current and new generation surveys.
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