Population III star formation in a Lambda CDM universe, II: Effects of a photodissociating background

Abstract

We examine aspects of primordial star formation in the presence of a molecular hydrogen-dissociating ultraviolet background. We compare a set of AMR hydrodynamic cosmological simulations using a single cosmological realization but with a range of ultraviolet background strengths in the Lyman-Werner band. This allows us to study the effects of Lyman-Werner radiation on suppressing H2 cooling at low densities as well as the high-density evolution of the collapsing core in a self-consistent cosmological framework. We find that the addition of a photodissociating background results in a delay of the collapse of high density gas at the center of the most massive halo in the simulation and, as a result, an increase in the virial mass of this halo at the onset of baryon collapse. We find that, contrary to previous results, Population III star formation is not suppressed for J${}_{21}\ge 0.1$, but occurs even with backgrounds as high as J${}_{21}=1$. We find that H2 cooling leads to collapse despite the depressed core molecular hydrogen fractions due to the elevated H2 cooling rates at $T=2-5\times 10^3$ K. We observe a relationship between the strength of the photodissociating background and the rate of accretion onto the evolving protostellar cloud core, with higher LW background fluxes resulting in higher accretion rates. Finally, we find that the collapsing halo cores in our simulations do not fragment at densities below $n\sim 10^{10}$ cm${}^{-3}$ regardless of the strength of the LW background, suggesting that Population III stars forming in halos with T${}_{vir}\sim 10^4$ K may still form in isolation.

46 pages, 14 figures (9 color). Accepted by the Astrophysical Journal, some minor revisions

References in corpus (5)

• Early Cosmological HII/HeIII Regions and Their Impact on Second-Generation Star Formation
• Suppression of H_2 Cooling in the Ultraviolet Background
• The first generation of stars in LCDM cosmology
• The Transition from the First Stars to the Second Stars in the Early Universe
• Photodissociation feedback of Population III stars \\on their neighbor prestellar cores

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• Suppression of H_2 Cooling in the Ultraviolet Background
• Uncovering the Chemical Signature of the First Stars in the Universe
• Occurrence of Metal-free Galaxies in the Early Universe
• The formation of compact massive self-gravitating discs in metal-free haloes with virial temperatures of ~ 13000-30000 K
• Metal-Free Gas Supply at the Edge of Reionization: Late-Epoch Population III Star Formation
• Is H3+ cooling ever important in primordial gas?
• Reionization - A probe for the stellar population and the physics of the early universe
• On the minimum mass of reionization sources
• Dark stars: Implications and constraints from cosmic reionization and extragalactic background radiation
• Radiative Regulation of Population III Star Formation
• Open questions in the study of population III star formation