Dwarf galaxy formation with and without dark matter-baryon streaming velocities

TL;DR

This study investigates how baryon-dark matter streaming velocities influence early dwarf galaxy formation using cosmological hydrodynamic simulations, finding initial delays and suppression effects that diminish by redshift 5.

Contribution

It is the first detailed simulation-based analysis of the impact of baryon-dark matter streaming velocities on dwarf galaxy formation at high redshift.

Findings

Star formation delayed by ~50 Myr in streaming simulations

Number of luminous galaxies suppressed at high redshift in streaming runs

Effects of streaming velocities diminish by redshift 5, with galaxies showing similar properties at z=0

Abstract

We study how supersonic streaming velocities of baryons relative to dark matter -- a large-scale effect imprinted at recombination and coherent over $\sim 3$ Mpc scales -- affects the formation of dwarf galaxies at $z \gtrsim 5$. We perform cosmological hydrodynamic simulations, including and excluding streaming velocities, in regions centered on halos with $M_{\rm vir}(z=0) \approx 10^{10}$ M$_{\odot}$; 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 $M_{\rm vir} = 2\times10^{5}$ M$_{\odot}$ and $2\times10^9$ M$_{\odot}$ in the redshift range $z=20-5$. A few hundred of these galaxies form stars and have stellar masses ranging from 100 to $10^7$ M$_{\odot}$. 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 $z=0$.