Journal Article

The first galaxies: assembly, cooling and the onset of turbulence

Thomas H. Greif, Jarrett L. Johnson, Ralf S. Klessen and Volker Bromm

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 387, issue 3, pages 1021-1036
Published in print July 2008 | ISSN: 0035-8711
Published online June 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13326.x
The first galaxies: assembly, cooling and the onset of turbulence

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We investigate the properties of the first galaxies at z≳ 10 with highly resolved numerical simulations, starting from cosmological initial conditions and taking into account all relevant primordial chemistry and cooling. A first galaxy is characterized by the onset of atomic hydrogen cooling, once the virial temperature exceeds ≃104K, and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a ≃5 × 107M system by means of a detailed merger tree and derive an upper limit on the number of Population III (Pop III) stars formed prior to its assembly. We investigate the thermal and chemical evolution of infalling gas and find that partial ionization at temperatures ≳104K catalyses the formation of H2 and hydrogen deuteride, allowing the gas to cool to the temperature of the cosmic microwave background. Depending on the strength of radiative and chemical feedback, primordial star formation might be dominated by intermediate-mass Pop III stars formed during the assembly of the first galaxies. Accretion on to the nascent galaxy begins with hot accretion, where gas is accreted directly from the intergalactic medium and shock heated to the virial temperature, but is quickly accompanied by a phase of cold accretion, where the gas cools in filaments before flowing into the parent halo with high velocities. The latter drives supersonic turbulence at the centre of the galaxy and could lead to very efficient chemical mixing. The onset of turbulence in the first galaxies thus likely marks the transition to Pop II star formation.

Keywords: stars: early-type; stars: formation; galaxies: formation; galaxies: high-redshift; cosmology: theory; early Universe

Journal Article.  11443 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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