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

We study the baryonic, chemical and dynamical properties of a significantly large sample of early protogalaxies in the first 500 Myr of the Universe (redshift z greater than or similar to 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 haloes with dark matter mass M-DM > 2 x 10(6) M-circle dot. Early star-forming objects have: molecular fractions from x(mol) less than or similar to 10(-4) in quiescent structures up to x(mol) greater than or similar to 0.1 in active regions; star formation rates (SFR) similar to 10(-8)-10(-3) M-circle dot yr(-1); and metallicities in the range similar to 10(-8)-10(-2) Z(circle dot). Roughly similar to 10 per cent 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 similar to 10 Gyr(-1) at z similar to 9 and increasing with redshift up to similar to 10(2) Gyr(-1). Stellar feedback effects alter the baryonic content of the haloes and locally affect their chemical and thermodynamical 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 corotating, molecular-rich gas increases with cosmic time (from a few per cent at z similar to 20 up to similar to 5-15 per cent at z similar to 9), the chaotic nature of metal-enriched material does not lead to particular trends.