Galactic stellar halos have long been considered to contain fossil information on the early dynamical and chemical evolution of galaxies. We propose that the surface brightness distributions of old stellar halos contain the influence of reionization on early formation histories of galaxies. By assuming that reionization significantly suppresses star formation in small subgalactic clumps virialized after reionization redshift (zreion), we first numerically investigate how the structural and kinematical properties of stellar halos that formed from the merging of these subgalactic clumps depend on zreion. We then discuss what observable properties of galactic stellar halos offer us; we also discuss the fossil records of reionization influence on hierarchical formation of halos based on the current results of numerical simulations. We specifically suggest that both the half-light radius of stellar halos and the slope of their surface brightness profile contain useful information regarding the times in which star formation in subgalactic clumps were significantly influenced by reionization. By using the simulated surface brightness distributions of galactic stellar halos for models with different zreion, we also discuss how wide-field imaging studies of extragalactic halos will help us to elucidate the epoch of cosmic reionization.
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