Gas rich and gas poor structures through the stream velocity effect
  Using adiabatic high-resolution numerical simulations we quantify the effect
of the streaming motion of baryons with respect to dark matter at the time of
recombination on structure formation and evolution. Formally a second order
effect, the baryonic stream velocity has proven to have significant impact on
dark matter halo abundance, as well as on the gas content and morphology of
small galaxy clusters. In this work, we study the impact of stream velocity on
the formation and gas content of haloes with masses up to $10^9 M_{\odot}$, an
order of magnitude larger than previous studies. We find that the non-zero
stream velocity has a sizable impact on the number density of haloes with
masses $\lesssim$ few $\times 10^7 M_{\odot}$ up to $z=10$, the final redshift
of our simulations. Furthermore, the gas stream velocity induces a suppression
of the gas fraction in haloes, which at z=10 is $\sim 10 \%$ for objects with
$M\sim10^7M_{\odot}$, as well as a flattening of the gas density profiles in
the inner regions of haloes. We further identify and study the formation, in
the context of a non-zero stream velocity, of moderately long lived gas
dominated structures at intermediate redshifts $10 < z < 20$, which Naoz and
Narayan have recently proposed as potential progenitors of globular clusters.
