• cosmic background radiation;
  • cosmology: theory;
  • dark ages, reionization, first stars;
  • large-scale structure of Universe


The number count of ionized bubbles on a map of 21-cm fluctuations with the primordial non-Gaussianity is investigated. The existence of the primordial non-Gaussianity modifies the re-ionization process, because the formation of collapsed objects, which could be the source of re-ionization photons, is affected by the primordial non-Gaussianity. In this paper, the abundance of ionized bubbles is calculated by using a simple analytic model with the local type of the primordial non-Gaussianity, which is parametrized by fNL. In order to take into account the dependence of the number count on the size of ionized bubbles and the resolution of the observation instrument, a threshold parameter Bb which is related to the the surface brightness temperature contrast of an ionized bubble is introduced. We show the potential to put the constraint on fNL from the number count by future observations such as Low Frequency Array (LOFAR) and Square Kilometre Array (SKA).