Morphology parameters: substructure identification in X-ray galaxy clusters

Abstract

Context. In recent years multi-wavelength observations have shown the presence of substructures related to merging events in a large proportion of galaxy clusters. Clusters can be roughly grouped into two categories -relaxed and non-relaxed -and a proper characterisation of the dynamical state of these systems is crucial for both astrophysical and cosmological studies. Aims. In this paper we investigate the use of a number of morphological parameters (Gini, M 20 , concentration, asymmetry, smoothness, ellipticity, and Gini of the second-order moment, G M ) introduced to automatically classify clusters as relaxed or dynamically disturbed systems. Methods. We apply our method to a sample of clusters at different redshifts extracted from the Chandra archive and investigate possible correlations between morphological parameters and other X-ray gas properties. Results. We conclude that a combination of the adopted parameters is a very useful tool for properly characterising the X-ray cluster morphology. According to our results, three parameters -Gini, M 20 , and concentration -are very promising for identifying cluster mergers. The Gini coefficient is a particularly powerful tool, especially at high redshift, because it is independent of the choice of the position of the cluster centre. We find that high Gini (>0.65), high concentration (>1.55), and low M 20 (<-2.0) values are associated with relaxed clusters, while low Gini (<0.4), low concentration (<1.0), and high M 20 (>-1.4) characterise dynamically perturbed systems. We also estimate the X-ray cluster morphological parameters in the case of radio loud clusters. Since they are in excellent agreement with previous analyses we confirm that diffuse intracluster radio sources are associated with major mergers.

Aging haloes: implications of the magnitude gap on conditional statistics of stellar and gas properties of massive haloes

“…In principle, this analysis can be extended to dynamical state and other formation time proxies. For example, the distribution and morphological properties of hot gas, which are observable through X-ray and millimeter wavelenghts, can inform us about the dynamical state and the assembly history of cluster (Parekh et al 2015). The X-ray luminosity and temperature of hot gas depend on the assembly history of the clusters (Hartley et al 2008;Fujita et al 2018).…”

Searching for Bulk Motions in the Intracluster Medium of Massive, Merging Clusters With Chandra CCD Data

“…The exposure times in the fourth column correspond to the effective values after data reduction. Optical redshift references: (1) Parekh et al (2015), (2 Note.The observing mode is VFAINT for all of the ObsID. The exposure times in the fourth column correspond to the effective values after data reduction.…”

Connecting optical and X-ray tracers of galaxy cluster relaxation

“…Yahil & Vidal 1977;Bird & Beers 1993;Hou et al 2009;Martínez & Zandivarez 2012), and diffuse X-ray emission which is symmetric about the group/cluster centre (e.g. Rasia et al 2013;Weißmann et al 2013;Parekh et al 2015). The dynamical state of clusters is related to the age of the halo and the time since infall for member galaxies, which simulations have shown is an important quantity in determining the degree to which galaxy properties are affected by environment (e.g.…”