First Pop III stars are believed to form inside minihalos (T<10^4 K) <br /><br />
with the help of hydrogen molecule (H_2) cooling. H_2, however, is <br /><br />
easily dissociated by H_2 Lyman-Werner band photons, which can originate <br /><br />
from sources in cosmological distance. We calculate the build-up of this <br /><br />
H_2 dissociating background during the epoch of reionization, based upon <br /><br />
the recent cosmic reionization simulation results. We show that (1) H_2 <br /><br />
dissociating background builds up long before the end of cosmic <br /><br />
reionization and (2) due to the clustering of sources of reionization, <br /><br />
the resultant background shows a significant spatial fluctuation. This <br /><br />
would lead to a spatial variation of the formation of Pop III objects. <br /><br />
The observational perspective (e.g. JWST observation) of our result is <br /><br />
also presented.