Journal Article

The interplay between chemical and mechanical feedback from the first generation of stars

Umberto Maio, Sadegh Khochfar, Jarrett L. Johnson and Benedetta Ciardi

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 2, pages 1145-1157
Published in print June 2011 | ISSN: 0035-8711
Published online June 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18455.x
The interplay between chemical and mechanical feedback from the first generation of stars

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We study cosmological simulations of early structure formation, including non-equilibrium molecular chemistry, metal pollution from stellar evolution, transition from Population III (PopIII) to Population II (PopII) star formation, regulated by a given critical metallicity, and feedback effects. We perform analyses of the properties of the gas, and use the PopIII and PopII populations as tracers of the metallicity. This allows us to investigate the properties of early metal spreading from the different stellar populations and its interplay with pristine molecular gas, in terms of the initial mass function and critical metallicity. We find that, independently of the details about PopIII modelling, after the onset of star formation, regions enriched below the critical level are mostly found in isolated environments, while PopII star formation regions are much more clumped. Typical star-forming haloes, at z∼ 15–10, with masses between ∼107 and 108 M, show average supernova (SN) driven outflow rates of up to ∼10−4 M yr−1 in enriched gas, initially leaving the original star formation regions almost devoid of metals. The polluted material, which is gravitationally incorporated in overdense environments on time-scales of ∼107 yr, is mostly coming from external, nearby star-forming sites (‘gravitational enrichment’). In parallel, the pristine-gas inflow rates are some orders of magnitudes larger, between ∼10−3 and 10−1 M yr−1. However, thermal feedback from SN destroys molecules within the pristine gas hindering its ability to cool and to condense into high-density star-forming regions. Only the polluted material incorporated via gravitational enrichment can continue to cool by atomic fine-structure transitions on short time-scales, short enough to end the initial PopIII regime within less than 108 yr. Moreover, the interplay between the pristine, cold, infalling gas and the ejected, hot, metal-rich gas leads to turbulent Reynolds numbers of the order of ∼108–1010, and contributes to the suppression of pristine inflow rates into the densest, star-forming regions.

Keywords: galaxies: formation; galaxies: high-redshift; cosmology: theory; dark ages, reionization, first stars; early Universe

Journal Article.  9209 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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