Bulk Flows and End of the Dark Ages with the SKA

TL;DR

This paper explores how primordial bulk flows in the early Universe affected star formation, metal spreading, and re-ionization, and discusses how the upcoming SKA telescope can detect these effects through HI and molecular line observations.

Contribution

It provides analytical and simulation-based insights into the impact of primordial bulk flows on early baryon evolution and highlights SKA's potential to observe these effects.

Findings

Bulk flows can delay star formation and metal spreading.

They cause patchier and noisier HI signals during re-ionization.

SKA will probe effects at high redshifts (z ~ 6-40).

Abstract

The early Universe is a precious probe of the birth of primordial objects, first star formation events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation of coherent supersonic gaseous streaming motions at decoupling time. These bulk flows impact the gas cooling process and determine a cascade effect on the whole baryon evolution. By analytical estimates and N-body hydrodynamical chemistry numerical simulations including atomic and molecular evolution, gas cooling, star formation, feedback effects and metal spreading for individual species from different stellar populations according to the proper yields and lifetimes, we discuss the role of these primordial bulk flows at the end of the dark ages and their detectable impacts during the first Gyr in view of the upcoming SKA mission. Early bulk flows can inhibit molecular gas cooling capabilities, suppressing star formation, metal spreading and the abundance of small primordial galaxies in the infant Universe. This can determine a delay in the re-ionization process and in the heating of neutral hydrogen making the observable HI signal during cosmic evolution patchier and noisier. The planned SKA mission will represent a major advance over existing instruments, since it will be able to probe the effects on HI 21cm at z ~ 6-20 and on molecular line emissions from first collapsing sites at z ~ 20-40. Therefore, it will be optimal to address the effects of primordial streaming motions on early baryon evolution and to give constraints on structure formation in the first Gyr.