EPoS Contribution
EPoS Contribution
A simple and accurate chemical network for hydrogen and carbon chemistry in the ISM

Munan Gong
Princeton U, Princeton, US
Chemistry plays an important role in star formation, regulating heating and cooling of the gas, and determining abundances of molecular species that trace gas properties in observations. Although solving the time-dependent equations is necessary for accurate abundances and temperature in the dynamic interstellar medium (ISM), a full chemical network is too computationally expensive to incorporate in numerical simulations. In this paper, we propose a new simplified chemical network for hydrogen and carbon chemistry in the atomic and molecular interstellar medium. We compare our chemical network in detail with results from a photo-dissociation region (PDR) code, and also with the NL99 network previously adopted in the simulation literature. We show that our chemical network gives similar results to the PDR code in the equilibrium abundances of all species over a wide range of densities, whereas the NL99 network shows significant disagreement. Applying our network in 1D models, we find that the temperature of CO tracks the cosmic-ray ionization rate in molecular clouds, and provide a simple fit for the locus of CO dominated regions. We also construct a simple model to calculate the composition of turbulent molecular clouds with slab and spherical geometry.
Caption: Column density of different species as a function of hydrogen column/visual extinction in one-dimensional one-sided uniform slab with density nH = 100 cm-3. Different line-styles represent results using our network (solid lines), the PDR code (dashed lines), and the NL99 network (dotted lines). Note that the NL99 network substantially underestimates the CO column.
E.C. Ostriker, Princeton U, US
M.G. Wolfire, U Maryland, US
Suggested Session: Chemistry