The complexity that the first stars brought to the Universe: Fragility of metal enriched gas in a radiation field

Abstract

The initial mass function (IMF) of the first (Population III) stars and Population II (Pop II) stars is poorly known due to a lack of observations of the period between recombination and reionization. In simulations of the formation of the first stars, it has been shown that, due to the limited ability of metal-free primordial gas to cool, the IMF of the first stars is a few orders of magnitude more massive than the current IMF. The transition from a high-mass IMF of the first stars to a lower-mass current IMF is thus important to understand. To study the underlying physics of this transition, we performed several simulations using the cosmological hydrodynamic adaptive mesh refinement code Enzo for metallicities of 10^{-4}, 10^{-3}, 10^{-2}, and 10^{-1} Z_{\odot}. In our simulations we include a star formation prescription that is derived from a metallicity dependent multi-phase ISM structure, an external UV radiation field, and a mechanical feedback algorithm. We also implement cosmic ray heating, photoelectric heating and gas-dust heating/cooling, and follow the metal enrichment of the ISM. It is found that the interplay between metallicity and UV radiation leads to the co-existence of Pop III and Pop II star formation in non-zero metallicity (Z/Z_{\odot} \geq10^{-2}) gas. A cold (T<100 K) and dense (ρ>10^{-22} g cm^{-3}) gas phase is fragile to ambient UV radiation. In a metal-poor (Z/Z_{\odot} \leq10^{-3}) gas, the cold and dense gas phase does not form in the presence of a radiation field of F_{0}\sim10^{-5}-10^{-4} erg cm^{-2} s^{-1}. Therefore, metallicity by itself is not a good indicator of the Pop III-Pop II transition. Metal-rich (Z/Z_{\odot}\geq10^{-2}) gas dynamically evolves two to three orders of magnitude faster than metal poor gas (Z/Z_{\odot}\leq10^{-3}). The simulations including SNe show that pre-enrichment of the halo does not affect the mixing of metals.

Published in ApJ

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Cited by in corpus (14)

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• Revisiting The First Galaxies: The epoch of Population III stars
• Molecular cooling in the diffuse interstellar medium
• Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first stellar cluster
• Star formation near an obscured AGN: Variations in the initial mass function
• Low-metallicity star formation: Relative impact of metals and magnetic fields
• Thermal instability and multi-phase interstellar medium in the first galaxies
• The implications of dust for high-redshift protogalaxies and the formation of binary disks
• The Response of Metal Rich Gas to X-Ray Irradiation from a Massive Black Hole at High Redshift: Proof of Concept
• Ultra-faint dwarf galaxies as a test of early enrichment and metallicity-dependent star formation
• Formation of the First Galaxies: Theory and Simulations
• High-Performance Astrophysical Simulations and Analysis with Python