Ionization Front Instabilities in Primordial H II Regions

Abstract

Radiative cooling by metals in shocked gas mediates the formation of ionization front instabilities in the galaxy today that are responsible for a variety of phenomena in the interstellar medium, from the morphologies of nebulae to triggered star formation in molecular clouds. An important question in early reionization and chemical enrichment of the intergalactic medium is whether such instabilities arose in the H II regions of the first stars and primeval galaxies, which were devoid of metals. We present three-dimensional numerical simulations that reveal both shadow and thin-shell instabilities readily formed in primordial gas. We find that the hard UV spectra of Population III stars broadened primordial ionization fronts, causing H2 formation capable of inciting violent thin- shell instabilities in D-type fronts, even in the presence of intense Lyman-Werner flux. The high post- front gas temperatures associated with He ionization sustained and exacerbated shadow instabilities, unaided by molecular hydrogen cooling. Our models indicate that metals eclipsed H2 cooling in I-front instabilities at modest concentrations, from 0.001- 0.01 solar. We conclude that ionization front instabilities were prominent in the H II regions of the first stars and galaxies, influencing the escape of ionizing radiation and metals into the early universe.

13 pages, 11 figures, accepted by ApJ with minor revisions

References in corpus (6)

• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• Early Cosmological HII/HeIII Regions and Their Impact on Second-Generation Star Formation
• The HII Region of a Primordial Star
• Does Radiative Feedback by the First Stars Promote or Prevent Second Generation Star Formation?
• Three-Dimensional Dynamical Instabilities in Galactic Ionization Fronts
• Formation of Pillars at the Boundaries between H II Regions and Molecular Clouds

Cited by in corpus (8)

• Resolving the Formation of Protogalaxies. III. Feedback from the First Stars
• The Destruction of Cosmological Minihalos by Primordial Supernovae
• TRAPHIC - Radiative Transfer for Smoothed Particle Hydrodynamics Simulations
• How Very Massive Metal Free Stars Start Cosmological Reionization
• How the First Stars Regulated Local Star Formation I: Radiative Feedback
• The Fate of the First Galaxies. III. Properties of Primordial Dwarf Galaxies and their Impact on the Intergalactic Medium
• The Molecular Hydrogen Deficit in Gamma-Ray Burst Afterglows
• Formation Criteria and the Mass of Secondary Population III Stars