Temperature fluctuations in H II regions: t2 for the two-phase model

Abstract

Aims: We investigate temperature fluctuations in H II regions in terms of a two-phase model, which assumes that the nebular gas consists of a hot and a cold phase. Methods: We derive general formulae for T([O III), the [O III] forbidden line temperature, and T(H I), the hydrogen Balmer jump temperature, in terms of the temperatures of the hot and cold phases, T_h and T_c. Results: For large temperature differences, the values of t2 required to account for the observed difference between T([O III]) and T(H I) are much lower than those deduced using the classical formulae that assume random and small amplitude temperature fluctuations. One should therefore be cautious when using a two-phase model to account for empirically derived $t^2$ values. We present a correction of a recent work by Giammanco & Beckman, who use a two-phase model to estimate the ionization rate of H II regions by cosmicrays. We show that a very small amount of cold gas is sufficient to account for t2 values typically inferred for H II regions.

arXiv comment5 pages, 1 figure, accepted for publication in A&A

References in corpus (4)

• Optical Recombination Lines of Heavy-elements in Giant Extragalactic HII Regions
• Helium recombination spectra as temperature diagnostics for planetary nebulae
• The electron temperature in ionized nebulae
• Temperature fluctuations in HII regions: ionization by Cosmic Rays as a key mechanism

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• Three-dimensional chemically homogeneous and bi-abundance photoionization models of the "super-metal-rich" planetary nebula NGC 6153
• Electron Energy Distributions in HII Regions and Planetary Nebulae: kappa-Distributions Do Not Apply
• Nonextensive thermal sources of cosmic rays?