The Formation of Supermassive Black Holes from Low-Mass Pop III Seeds
  The existence of 10$^9$ M$_{\odot}$ black holes (BH) in massive galaxies by
$z \ sim$ 7 is one of the great unsolved mysteries in cosmological structure
formation. One theory argues that they originate from the black holes of Pop
III stars at $z \sim$ 20 and then accrete at the Eddington limit down to the
epoch of reionization, which requires that they have constant access to rich
supplies of fuel. Because early numerical simulations suggested that Pop III
stars were $\gtrsim$ 100 M$_{\odot}$, the supermassive black hole seeds
considered up to now were 100 - 300 M$_{\odot}$. However, there is a growing
numerical and observational consensus that some Pop III stars were tens of
solar masses, not hundreds, and that 20 - 40 M$_{\odot}$ black holes may have
been much more plentiful at high redshift. However, we find that natal kicks
imparted to 20 - 40 M$_{\odot}$ Pop III BHs during formation eject them from
their halos and hence their fuel supply, precluding them from Eddington-limit
growth. Consequently, supermassive black holes are far less likely to form from
low-mass Pop III stars than from very massive ones.
