REU Supplement: Numerical simulations of non-equilibrium plasmas and their spectra - extensions to the molecular environs of AGN & Starburst Galaxies

Grants and Contracts Details


C.1 The microphysics of a non-equilibrium gas Most of the quantitative information we have about the cosmic comes from the analysis of spectra. Astronomical environments generally have low densities. ~H < 1018 cm3, and are exposed to light and particles with a variety of energies. The physical conditions in the gas are highly non-equilibrium as a result. The spectrum, the only way we can measure properties of the source, is set by a host of microphysical processes rather than by simple thermodynamic relations. The atomic and molecular physics is a complication but is also why the spectrum reveals so much. New generations of instruments such as Alma and next-generation optical/IR telescopes will measure spectra with high resolution and sensitivity at very high redshift. We must develop the tools to understand these spectra. This proposal is for continued support for the development and application of the spectral synthesis code Cloudy. It is a community code designed to fully simulate the microphysics of a non-equilibrium gas, determine its microscopic properties, and predict the resulting spectrum. Although the code was originally designed to simulate conditions in the inner regions of quasars, it has been extended to conditions ranging from cold and molecular to hot and ionized, from the CMB temperature to IO~° K, and densities from the low density limit to LIE. Cloudy is designed to treat the fill microphysics of the gas and dust without compromise. It does not use simple fitting formulae such as "universal" gas-cooling or grain-heating functions. Rather, atomic and molecular processes are simulated in detail. In this approach we build from microscopic into the macroscopic. The final result might be a full simulation of the properties and spectrum of the broad-line region of a quasar, an intergalactic cloud, or a galactic molecular cloud. Although the macroscopic environments are quite different the microphysics is the same. This proposal is a multi-pronged effort with the common theme of understanding star-forming regions and active galaxies. The most massive stars, which emit hydrogen-ionizing radiation, are too short-lived for them to stray far from the molecular clouds where they formed. Starlight creates a photoablative layer on the surface of the molecular cloud. Hydrogen in the outermost layer, the H II region, is ionized (H4). Ionizing starlight is extinguished by gas and dust opacities creating a deeper layer where hydrogen is H°, the PDR. Hydrogen and many other elements become molecular in regions which are most shielded from radiation. These Ht'H°/H2 layers form a single physical entity, rather than three distinct problems, and we are developing the theoretical tools to consider them this way. A major emphasis of this proposal is to understand the conditions in filaments surrounding the central galaxy in cool-core clusters of galaxies. The total mass of the filaments in the Perseus cluster is -4x10'° ~ (Salomd et al 2006) showing that they are a significant component of the cluster environment. Their origin is unknown and their physical conditions are unlike those seen in any galactic nebula. The optical spectra have strong low-ionization lines. The N IJ fl5 199 doublet is nearly as strong as the Balmer lines. This line is very faint in galactic photoionized nebulae because of the nature of a photoionized cloud, The near IR spectrum reveals 112 lines that are nearly as bright as neighboring Paschen lines. Radio CO lines are strong and HCN have been detected (Salome et al 2008). Many filaments have resisted star formation for times of several Gyr (Hatch et al. 2006). These filaments pose a number of questions at the intersection of star formation and molecularlionic physics. They have many, but not all, properties in common with filaments in the Crab Nebula, We will use these exotic environments to test the behavior of gas and dust under extremes of suprathermal particle, cosmic ray, and high-energy radiation.
Effective start/end date6/10/118/31/12


  • National Science Foundation


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