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Star formation and molecular hydrogen in dwarf galaxies: a non-equilibrium view

Hu, Chia-Yu, Naab, Thorsten, Walch, Stefanie, Glover, Simon C. O. and Clark, Paul 2016. Star formation and molecular hydrogen in dwarf galaxies: a non-equilibrium view. Monthly Notices of the Royal Astronomical Society 458 (4) , pp. 3528-3553. 10.1093/mnras/stw544

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Abstract

We study the connection of star formation to atomic (H I) and molecular hydrogen (H2) in isolated, low-metallicity dwarf galaxies with high-resolution (mgas = 4 M, Nngb = 100) smoothed particle hydrodynamics simulations. The model includes self-gravity, nonequilibrium cooling, shielding from a uniform and constant interstellar radiation field, the chemistry of H2 formation, H2-independent star formation, supernova feedback and metal enrichment. We find that the H2 mass fraction is sensitive to the adopted dust-to-gas ratio and the strength of the interstellar radiation field, while the star formation rate is not. Star formation is regulated by stellar feedback, keeping the gas out of thermal equilibrium for densities n < 1 cm−3. Because of the long chemical time-scales, the H2 mass remains out of chemical equilibrium throughout the simulation. Star formation is well correlated with cold (T ≤ 100 K) gas, but this dense and cold gas – the reservoir for star formation – is dominated by H I, not H2. In addition, a significant fraction of H2 resides in a diffuse, warm phase, which is not star-forming. The interstellar medium is dominated by warm gas (100 K < T ≤ 3 × 104 K) both in mass and in volume. The scaleheight of the gaseous disc increases with radius while the cold gas is always confined to a thin layer in the mid-plane. The cold gas fraction is regulated by feedback at small radii and by the assumed radiation field at large radii. The decreasing cold gas fractions result in a rapid increase in depletion time (up to 100 Gyr) for total gas surface densities H I+H2 10 M pc−2, in agreement with observations of dwarf galaxies in the Kennicutt–Schmidt plane.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Publisher: Oxford University Press
ISSN: 00358711
Date of First Compliant Deposit: 1 September 2017
Date of Acceptance: 3 March 2016
Last Modified: 01 Sep 2017 16:07
URI: http://orca.cf.ac.uk/id/eprint/104237

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