Are galaxies extending?
  It is suggested that the recently observed size evolution of very massive compact galaxies in the early universe can be explained, if dark matter is in Bose Einstein condensate.   In this model the size of the dark matter halos and galaxies depends on the correlation length of dark matter and, hence, on the the expansion of the universe. This theory predicts that the size of the galaxies increases as the Hubble radius of the universe even without merging, which agrees well with the recent observational data. 
Jae-Weon Lee