A Supra-galactic Conundrum: The Globular Clusters Colour Pattern in
  Virgo Galaxies
  The presence of systematic modulations in the colour distributions in
composite samples of globular clusters associated with galaxies in the Virgo
and Fornax clusters has been reported in a previous work. In this paper we
focus on the 27 brightest galaxies in Virgo, and in particular on NGC 4486, the
dominant system in terms of globular cluster population. The new analysis
includes $\sim$7600 cluster candidates brighter than g =24.5 (or T1$\sim$
23.70). The results indicate the presence of the characteristic Virgo pattern
in these galaxies and that this pattern is detectable over a galactocentric
range from 3 to 30 Kpc in N GC 4486. This finding gives more support to the
idea that the pattern has been the result of an external, still not identified
phenomenon, capable of synchronizing the cluster formation in a kind of viral
process, and on supra-galactic scales (also having, presumably, an impact on
the overall star formation history in the entire Virgo cluster).
