The Three Hundred project: quest of clusters of galaxies morphology and dynamical state through Zernike polynomials

Abstract

The knowledge of the dynamical state of galaxy clusters allows to alleviate systematics when observational data from these objects are applied in cosmological studies. Evidence of correlation between the state and the morphology of the clusters is well studied. The morphology can be inferred by images of the surface brightness in the X-ray band and of the thermal component of the Sunyaev-Zel’dovich (tSZ) effect in the millimetre range. For this purpose, we apply, for the first time, the Zernike polynomial decomposition, a common analytic approach mostly used in adaptive optics to recover aberrated radiation wavefronts at the telescopes pupil plane. With this novel way we expect to correctly infer the morphology of clusters and so possibly, their dynamical state. To verify the reliability of this new approach we use more than 300 synthetic clusters selected in THE THREE HUNDRED project at different redshifts ranging from 0 up to 1.03. Mock maps of the tSZ, quantified with the Compton parameter, y-maps, are modelled with Zernike polynomials inside R500, the cluster reference radius. We verify that it is possible to discriminate the morphology of each cluster by estimating the contribution of the different polynomials to the fit of the map. The results of this new method are correlated with those of a previous analysis made on the same catalogue, using two parameters that combine either morphological or dynamical-state probes. We underline that instrumental angular resolution of the maps has an impact mainly when we extend this approach to high-redshift clusters.

Morphological analysis of SZ and X-ray maps of galaxy clusters with Zernike polynomials

“…For example, very regular patterns, mostly circular, can be related to relaxed systems, while asymmetries and substructures are signals of a disturbed dynamical state. In [4] we analyzed mock Compton parameter maps at high resolution (see Sect. 3) and within a circular aperture of radius equal to R 500 , therefore we used ZPs up to the eight order n (i.e.…”

“…3) and within a circular aperture of radius equal to R 500 , therefore we used ZPs up to the eight order n (i.e. 45 terms, see the ordering scheme in [6]) in order to obtain a spatial resolution of ⇠ 0.5R 500 in the modelling (see also Appendix A in [4]). We divided the ZPs in two classes, based on their 2D projections: terms with m = 0, which show a circular symmetry and terms with m , 0, which fit azimuthal inhomogeneities.…”

“…y-maps) which characterizes the e↵ect. They were mimicked with the PyMSZ code 1 [7], with a spatial resolution of 10 kpc per pixel corresponding to angular resolutions of 5.25 00 , 1.14 00 and 0.59 00 respectively at z = 0, 0.45 and 1.03, the reference redshifts analysed in [4]. We normalized each map to the maximum and performed the Zernike fitting within a circular aperture of radius R 500 centred on the y-centroid.…”

“…Here, we report a new approach to the morphological analysis, developed in [4], which consists in modelling the cluster images with a set of functions, the Zernike polynomials (ZPs). This new method was validated, at first, on mock projections maps realized by exploiting the Sunyaev-Zel'dovich (SZ) e↵ect [5], i.e.…”

The Three Hundred Project: The stellar angular momentum evolution of cluster galaxies

“…We approach these issues by analysing simulations from The Three Hundred project 1 , that is a sample of over 300 galaxy clusters simulated with full-physics hydrodynamics (Cui et al 2018). These simulated clusters have been used for different studies, for example, environmental effects (Wang et al 2018), cluster profiles (Mostoghiu et al 2019;Li et al 2020;Baxter et al 2021), backsplash galaxies (Arthur et al 2019;Haggar et al 2020;Knebe et al 2020), the cluster dynamical state (Capalbo et al 2021;De Luca et al 2021), filament structures (Kuchner et al 2020(Kuchner et al , 2021Rost et al 2021), and gravitational lensing (Vega-Ferrero et al 2021). In this work we extend the previous stellar angular momentum analysis to this set of massive simulated galaxy clusters to study the influence of the cluster environment on the stellar kinematics of infalling galaxies.…”