Title:   An analytical model of the large neutral regions during the late stage

       of reionization 

       Speaker: Yidong Xu (NAOC) 

　　Time: 2:00 pm, April 1 (Tuesday) 

　　Location: 3rd floor, small conf. room 

　　Abstract: 

　　In this talk, we will discuss the nature and distribution of large neutral regions during the late epoch of reionization. In the "bubble model" of reionization, the mass distribution of large ionized regions ("bubbles") during the early stage of reionization is obtained by using the excursion set model, where the ionization of a region corresponds to the first up-crossing of a barrier by random trajectories. We generalize this idea, and develop a method to predict the distribution of large scale neutral regions during the late stage of reionization, taking into account the ionizing background after the percolation of HII regions. The large scale neutral regions which we call "neutral islands" are not individual galaxies or minihalos, but larger regions where fewer galaxies formed and hence ionized later, and they are identified in the excursion set model with the first down-crossings of the island barrier. Assuming that the consumption rate of ionizing background photons is proportional to the surface area of the neutral islands, we obtained the size distribution of the neutral islands. We also take the "bubbles-in-island" effect into account, and find that this effect is very important. An additional barrier is set to avoid islands being percolated through. We will present our model results of neutral islands scales, their evolution, and the late reionization process.