  First, the formation of first objects driven by dark matter is revisited by
high-resolution hydrodynamic simulations. It is revealed that dark matter
haloes of ~10^4M_sun can produce first luminous objects with the aid of dark
matter cusps. Therefore, the mass of first objects is smaller by roughly two
orders of magnitude than in the previous prediction. This implies that the
number of Pop III stars formed in the early universe could be significantly
larger than hitherto thought. Secondly, the feedback by photo-ionization and
photo-dissociation photons in the first objects is explored with radiation
hydrodynamic simulations, and it is demonstrated that multiple stars can form
in a 10^5M_sun halo. Thirdly, the fragmentation of an accretion disk around a
primordial protostar is explored with photo-dissociation feedback. As a result,
it is found that the photo-dissociation can reduce the mass accretion rate onto
protostars. Also, protostars as small as 0.8M_sun may be ejected and evolve
with keeping their mass, which might be detected as "real first stars" in the
Galactic halo. Finally, state-of-the-art radiation hydrodynamic simulations are
performed to investigate the internal ionization of first galaxies and the
escape of ionizing photons. We find that UV feedback by forming massive stars
enhances the escape fraction even in a halo as massive as > 6* 10^9M_sun, while
it reduces the star formation rate significantly. This may have a momentous
impact on the cosmic reionization.
