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 109 M⊙, 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 ≲ few × 107 M⊙ 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 ∼10 per cent for objects with M ∼ 107 M⊙, 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.