The formation of direct collapse black holes under the influence of
  streaming velocities
  We study the influence of a high baryonic streaming velocity on the formation
of direct collapse black holes (DCBHs) with the help of cosmological
simulations carried out using the moving mesh code {\sc arepo}. We show that a
streaming velocity that is as large as three times the root-mean-squared value
is effective at suppressing the formation of H$_{2}$-cooled minihaloes, while
still allowing larger atomic cooling haloes (ACHs) to form. We find that enough
H$_{2}$ forms in the centre of these ACHs to effectively cool the gas,
demonstrating that a high streaming velocity by itself cannot produce the
conditions required for DCBH formation. However, we argue that high streaming
velocity regions do provide an ideal environment for the formation of DCBHs in
close pairs of ACHs (the "synchronised halo" model). Due to the absence of star
formation in minihaloes, the gas remains chemically pristine until the ACHs
form. If two such haloes form with only a small separation in time and space,
then the one forming stars earlier can provide enough ultraviolet radiation to
suppress H$_{2}$ cooling in the other, allowing it to collapse to form a DCBH.
Baryonic streaming may therefore play a crucial role in the formation of the
seeds of the highest redshift quasars.
