The First Galaxies: Assembly, Cooling and the Onset of Turbulence

Abstract

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 10^4 K, and its ability to retain photoheated gas. We follow the complex accretion and star formation history of a 5*10^7 M_sun 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 > 10^4 K 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.

18 pages, 14 figures, published in MNRAS

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Cited by in corpus (10)

• Resolving the Formation of Protogalaxies. III. Feedback from the First Stars
• Accretion onto Intermediate-Mass Black Holes in Dense Protogalactic Clouds
• Chemical mixing in smoothed particle hydrodynamics simulations
• Reionization - A probe for the stellar population and the physics of the early universe
• The influence of magnetic fields on the thermodynamics of primordial star formation
• Dark stars: Implications and constraints from cosmic reionization and extragalactic background radiation
• First stars and the extragalactic background light: How recent gamma-ray observations constrain the early universe
• Angular momentum and clustering properties of early dark matter halos
• The formation of the first galaxies and the transition to low-mass star formation
• Open questions in the study of population III star formation