Observational evidence for bar formation in disk galaxies via
  cluster-cluster interaction
  Bars are an elongated structure that extends from the centre of galaxies, and
about one-third of disk galaxies are known to possess bars. These bars are
thought to form either through a physical process inherent in galaxies, or
through an external process such as galaxy-galaxy interactions. However, there
are other plausible mechanisms of bar formation that still need to be
observationally tested. Here we present the observational evidence that bars
can form via cluster-cluster interaction. We examined 105 galaxy clusters at
redshift $0.015 < z < 0.060$ that are selected from the Sloan Digital Sky
Survey data, and identified 16 interacting clusters. We find that the barred
disk-dominated galaxy fraction is about 1.5 times higher in interacting
clusters than in clusters with no clear signs of ongoing interaction (42%
versus 27%). Our result indicates that bars can form through a large-scale
violent phenomenon, and cluster-cluster interaction should be considered an
important mechanism of bar formation.
