Morphology parameters: substructure identification in X-ray galaxy
  clusters
  In recent years multi-wavelength observations have shown the presence of
substructures related to merging events in a high fraction 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 of
crucial importance both for astrophysical and cosmological studies.
  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. We apply our method to a sample of
clusters at different redshifts extracted from the {\it Chandra} archive and we
investigate possible correlations between morphological parameters and other
X-ray gas properties. We conclude that a combination of the adopted parameters
is a very useful tool to properly characterise 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, being independent
from 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 {\it radio loud} clusters. In excellent agreement with previous
analyses we confirm that diffuse intracluster radio sources are associated with
major mergers.
