Statistical properties of mass, star formation, chemical content and rotational patterns in early z > 9 structures

TL;DR

This study uses high-resolution simulations to analyze the properties of early proto-galaxies at redshifts greater than 9, revealing their star formation, chemical, and rotational characteristics during the first 500 million years of the universe.

Contribution

It provides detailed insights into the baryonic, chemical, and dynamical properties of early proto-galaxies, including star formation thresholds and rotational behavior, based on advanced numerical simulations.

Findings

First star formation occurs in halos with dark matter mass > 2×10^6 M_sun

Early star-forming objects show a wide range of molecular fractions and metallicities

Approximately 10% of high-z halos host Population II-I star formation, dominating the cosmic SFR density

Abstract

We study the baryonic, chemical and dynamical properties of a significantly large sample of early proto-galaxies in the first 500 Myr of the Universe (redshift z>9), obtained from high-resolution numerical, N-body, hydrodynamical, chemistry simulations including atomic and molecular networks, gas cooling, star formation, stellar evolution and metal spreading for population III and population II-I regimes according to proper stellar yields and lifetimes. We find that first star formation events take place in halos with dark-matter mass M_{DM} > 2\times 10^6 M_{sun}. Early star forming objects have: molecular fractions from x_{mol} < 10^{-4} in quiescent structures up to x_{mol} > 0.1 in active regions; star formation rates SFR ~10^{-8}-10^{-3}M_{sun}/yr; and metallicities in the range ~10^{-8}-10^{-2}Z_{sun}. Roughly ~10% of high-z haloes host population II-I star formation and dominate the cosmic SFR density. They usually are bursty objects with mean specific SFR around ~10 Gyr^{-1} at z~9 and increasing with redshift up to ~10^2 Gyr^{-1}. Stellar feedback effects alter the baryonic content of the haloes and locally affect their chemical and thermo-dynamical properties, as reflected by the broadening of various physical relations. The establishment of gaseous rotationally-supported cores is quite uncommon, weakly related to the large-scale dark-matter behaviour and evolving in an intermittent fashion. The colder, molecular-rich phase tends to maintain any established rotational motion longer with respect to the hotter, metal-rich component, which is very sensitive to environmental processes. While the fraction of haloes featuring a significant amount of co-rotating, molecular-rich gas increases with cosmic time (from a few percent at z~20 up to ~5-15% at z~9), the chaotic nature of metal-enriched material does not lead to particular trends.