Network analysis of the COSMOS galaxy field
  The galaxy data provided by COSMOS survey for 1 by 1 degree field of sky are
analysed by methods of complex networks. Three galaxy samples (slices) with
redshifts ranging within intervals 0.88-0.91, 0.91-0.94 and 0.94-0.97 are
studied as two-dimensional projections for the spatial distributions of
galaxies. We construct networks and calculate network measures for each sample,
in order to analyse the network similarity of different samples, distinguish
various topological environments, and find associations between galaxy
properties (colour index and stellar mass) and their topological environments.
Results indicate a high level of similarity between geometry and topology for
different galaxy samples and no clear evidence of evolutionary trends in
network measures. The distribution of local clustering coefficient C manifests
three modes which allow for discrimination between stand-alone singlets and
dumbbells (0 <= C <= 0.1), intermediately (0 < C < 0.9) and clique (0.9 <= C <=
1) like galaxies. Analysing astrophysical properties of galaxies (colour index
and stellar masses), we show that distributions are similar in all slices,
however weak evolutionary trends can also be seen across redshift slices. To
specify different topological environments we have extracted selections of
galaxies from each sample according to different modes of C distribution. We
have found statistically significant associations between evolutionary
parameters of galaxies and selections of C: the distribution of stellar mass
for galaxies with interim C differ from the corresponding distributions for
stand-alone and clique galaxies, and this difference holds for all redshift
slices. The colour index realises somewhat different behaviour.
