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Radiative feedback from populations II stars played a vital role in earlystructure formation. Particularly, photons below the Lyman limit can escape thestar forming regions and produce a background ultraviolet (UV) flux whichconsequently may influence the pristine halos far away from the radiationsources. These photons can quench the formation of molecular hydrogen byphoto-detachment of $\rm H^{-}$. In this study, we explore the impact of suchUV radiation on fragmentation in massive primordial halos of a few times $\rm10^{7}$~M${_\odot}$. To accomplish this goal, we perform high resolutioncosmological simulations for two distinct halos and vary the strength of theimpinging background UV field in units of $\rm J_{21}$. We further make use ofsink particles to follow the evolution for 10,000 years after reaching themaximum refinement level. No vigorous fragmentation is observed in UVilluminated halos while the accretion rate changes according to the thermalproperties. Our findings show that a few 100-10, 000 solar mass protostars areformed when halos are irradiated by $\rm J_{21}=10-500$ at $\rm z>10$ andsuggest a strong relation between the strength of UV flux and mass of aprotostar. This mode of star formation is quite different from minihalos, ashigher accretion rates of about $\rm 0.01-0.1$ M$_{\odot}$/yr are observed bythe end of our simulations. The resulting massive stars are the potentialcradles for the formation of intermediate mass black holes at earlier cosmictimes and contribute to the formation of a global X-ray background.

The formation of massive primordial stars in the presence of moderate UV backgrounds