The formation of massive primordial stars in the presence of moderate UV
  backgrounds
  Radiative feedback from populations II stars played a vital role in early
structure formation. Particularly, photons below the Lyman limit can escape the
star forming regions and produce a background ultraviolet (UV) flux which
consequently may influence the pristine halos far away from the radiation
sources. These photons can quench the formation of molecular hydrogen by
photo-detachment of $\rm H^{-}$. In this study, we explore the impact of such
UV radiation on fragmentation in massive primordial halos of a few times $\rm
10^{7}$~M${_\odot}$. To accomplish this goal, we perform high resolution
cosmological simulations for two distinct halos and vary the strength of the
impinging background UV field in units of $\rm J_{21}$. We further make use of
sink particles to follow the evolution for 10,000 years after reaching the
maximum refinement level. No vigorous fragmentation is observed in UV
illuminated halos while the accretion rate changes according to the thermal
properties. Our findings show that a few 100-10, 000 solar mass protostars are
formed when halos are irradiated by $\rm J_{21}=10-500$ at $\rm z>10$ and
suggest a strong relation between the strength of UV flux and mass of a
protostar. This mode of star formation is quite different from minihalos, as
higher accretion rates of about $\rm 0.01-0.1$ M$_{\odot}$/yr are observed by
the end of our simulations. The resulting massive stars are the potential
cradles for the formation of intermediate mass black holes at earlier cosmic
times and contribute to the formation of a global X-ray background.
