The CH+ Abundance in Turbulent, Diffuse Molecular Clouds

Abstract

The intermittent dissipation of interstellar turbulence is an important energy source in the diffuse ISM. Though on average smaller than the heating rates due to cosmic rays and the photoelectric effect on dust grains, the turbulent cascade can channel large amounts of energy into a relatively small fraction of the gas that consequently undergoes significant heating and chemical enrichment. In particular, this mechanism has been proposed as a solution to the long-standing problem of the high abundance of CH+ along diffuse molecular sight lines, which steady-state, low temperature models under-produce by over an order of magnitude. While much work has been done on the structure and chemistry of these small-scale dissipation zones, comparatively little attention has been paid to relating these zones to the properties of the large-scale turbulence. In this paper, we attempt to bridge this gap by estimating the temperature and CH+ column density along diffuse molecular sight-lines by post-processing 3-dimensional MHD turbulence simulations. Assuming reasonable values for the cloud density (30 / cm^3), size (20 pc), and velocity dispersion (2.3 km / s), we find that our computed abundances compare well with CH+ column density observations, as well as with observations of emission lines from rotationally excited H2 molecules.

13 pages, 10 figures, accepted by MNRAS

References in corpus (8)

• Theory of Star Formation
• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• Uncertainties in H2 and HD Chemistry and Cooling and their Role in Early Structure Formation
• Models of turbulent dissipation regions in the diffuse interstellar medium
• Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics
• On the enhanced cosmic-ray ionization rate in the diffuse cloud towards Zeta Persei
• Observational Properties of Rotationally Excited Molecular Hydrogen In Translucent Lines of Sight
• Modeling of diffuse molecular gas applied to HD 102065 observations

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