Schauer et al., available on arXiv

Abstract: We study how supersonic streaming velocities of baryons relative to dark matter — a large-scale effect imprinted at recombination and coherent over ~3 Mpc scales — affects the formation of dwarf galaxies at z>~5. We perform cosmological hydrodynamic simulations, including and excluding streaming velocities, in regions centered on halos with Mvir(z=0)~10^10 Msun; the simulations are part of the Feedback In Realistic Environments (FIRE) project and run with FIRE-3 physics. Our simulations comprise many thousands of systems with halo masses between Mvir=2×10^5 Msun and 2×10^9 Msun in the redshift range z=20−5. A few hundred of these galaxies form stars and have stellar masses ranging from 100 to 10^7 Msun. While star formation is globally delayed by approximately 50 Myr in the streaming relative to non-streaming simulations and the number of luminous galaxies is correspondingly suppressed at high redshift in the streaming runs, these effects decay with time. By z=5, the properties of the simulated galaxies are nearly identical in the streaming versus non-streaming runs, indicating that any effects of streaming velocities on the properties of galaxies at the mass scale of classical dwarfs and larger do not persist to z=0.