Cloudy: Modeling the Emission From Astrophysical Nebulae

G.J. Ferland
University of Kentucky

Session ID: T6.02   Type: oral

Abstract:

The emission line spectra of HII Regions, Planetary Nebulae, nova shells, Seyfert galaxies, and quasars contain quantitative information about the chemical composition of the emitting gas, and the luminosity of the central object. These lines are produced by warm gas with moderate to low density . Such gas is far from thermodynamic equilibrium and its physical conditions cannot be known from analytical theory. Rather, the observed spectrum is the result of a host of microphysical processes that must be numerically simulated in detail. I have been developing Cloudy, a large-scale code designed to simulate non-equilibrium plasmas and predict their spectra. The ionization, level populations, and electron temperature are determined as a function of depth by self-consistently solving the equations of statistical and thermal equilibrium. Lines and continua are optically thick and their transport must be treated in detail. Predictions of the intensities of thousands of lines and the column densities of all constituents result from the specification of only the incident continuum, gas density, and its composition. By their nature, such calculations involve enormous quantities of atomic/molecular data describing a host of microphysical processes, and the codes involved are at the forefront of modern computational astrophysics. We are witnessing first light of a large number of new optical to infrared observational facilities, and we will soon be in a position to obtain spectra of faint objects with unprecedented precision. The basic atomic data base is growing in both precision and size, and high-end workstations have the power of yesterday's s supercomputers. Large scale numerical simulations and spectral synthesis can now be done with unprecedented precision and facility, and provide a powerful analysis tool to complement these observational facilities.

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