The turbulent fragmentation of the interstellar medium: The impact of metallicity on global star formation

Abstract

We study the influence of gas metallicity, turbulence, and non-equilibrium chemistry on the evolution of the two-phase interstellar medium (warm and cold atomic phases), and thereby constrain the initial conditions for star formation prevailing in turbulent gas. We perform high-resolution simulations in three dimensions, including a realistic non-equilibrium treatment of the ionization state of the gas, and examine both driven and decaying turbulence. This allows us to explore variations in the metallicity Z. In this paper, we study solar metallicity, Z=Z_sun, and low metallicity, Z=1d-3 Z_sun, gas. For driven, large-scale turbulence, we find that the influence of the metallicity on the amount of mass in the cold gas component is small. However, in decaying turbulent conditions this picture is much changed. While cold regions survive in the case of solar metallicity, they are quickly heated and dispersed in low-metallicity gas. This result suggests that star formation can be suppressed in environments of low metallicity, unless a strong turbulent driver is acting on time scales shorter than a few turbulent crossing times. Inter alia this finding could explain the overall inefficient star formation as well as the burst-like mode of star formation found in metal-poor, gas-rich systems like dwarf galaxies.

17 pages, 6 figures, accepted for publication in ApJ

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• Physical Models of Galaxy Formation in a Cosmological Framework
• The SILCC (SImulating the LifeCycle of molecular Clouds) project: I. Chemical evolution of the supernova-driven ISM
• The SILCC (SImulating the LifeCycle of molecular Clouds) project - II. Dynamical evolution of the supernova-driven ISM and the launching of outflows
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• Star formation in metal-poor gas clouds
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• Thermal Phases of the Neutral Atomic Interstellar Medium -- from Solar Metallicity to Primordial Gas
• The Shapes of the HI Velocity Profiles of the THINGS Galaxies
• Impact of magnetic fields on ram pressure stripping in disk galaxies
• The effects of metallicity, UV radiation and non-equilibrium chemistry in high-resolution simulations of galaxies
• On the Indeterministic Nature of Star Formation on the Cloud Scale
• The role of magnetic fields in the structure and interaction of supershells
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• Evolution of dust and molecular hydrogen in the Magellanic System
• On the resolution requirements for modelling molecular gas formation in solar neighbourhood conditions
• 3D MHD astrospheres: applications to IRC-10414 and Betelgeuse
• Atomic Chemistry In Turbulent Astrophysical Media I: Effect of Atomic Cooling
• Galaxy Outflows Without Supernovae
• Study Turbulence and Probe Magnetic Field Using Gradients Technique: Application to HI-to-H2 Transition Regions
• Synthetic CO emission and the $X_{\mathrm{CO}}$ factor of young molecular clouds: a convergence study
• X-raying molecular clouds with a short flare: probing statistics of gas density and velocity fields
• Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM
• SILCC -- IX. The multi-phase interstellar medium at low metallicity