Statistical properties of mass, star formation, chemical content and rotational patterns in early z ≳ 9 structures
Abstract
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 ≳ 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 MDM > 2 × 106 M⊙. Early star-forming objects have: molecular fractions from xmol ≲ 10-4 in quiescent structures up to xmol ≳ 0.1 in active regions; star formation rates (SFR) ∼ 10-8-10-3 M⊙ yr-1; and metallicities in the range ∼10-8-10-2 Z⊙. Roughly ∼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 ∼10 Gyr-1 at z ∼ 9 and increasing with redshift up to ∼102 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 ∼ 20 up to ∼5-15 per cent at z ∼ 9), the chaotic nature of metal-enriched material does not lead to particular trends.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2013
- DOI:
- 10.1093/mnras/stt1678
- arXiv:
- arXiv:1309.2283
- Bibcode:
- 2013MNRAS.436.1621B
- Keywords:
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- methods: numerical;
- cosmology: theory;
- early Universe;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 20 pages, 19 figures