Gas rich and gas poor structures through the stream velocity effect

TL;DR

This study uses high-resolution simulations to analyze how baryonic stream velocity affects the formation, abundance, and gas content of dark matter haloes and small galaxy clusters, revealing significant impacts on structure evolution.

Contribution

It extends previous work by examining larger halo masses and higher redshifts, demonstrating the substantial influence of stream velocity on halo properties and potential globular cluster progenitors.

Findings

Stream velocity reduces halo abundance for masses below a few 10^7 M_sun at z=10.

Gas fraction in haloes is suppressed by about 10% at z=10 for 10^7 M_sun objects.

Formation of long-lived gas-rich structures potentially linked to globular clusters is observed.

Abstract

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.