Cloudy: Numerical Simulations of Plasmas and their Spectra If a picture is worth a thousand words, a spectrum is worth a thousand pictures Understanding Starburst Galaxies - Numerical Simulations of Diffuse Interstellar Gas Gary Ferland, Nick Abel, Ryan Porter, Gargi Shaw UK Physics

Cloudy: Numerical Simulations of Plasmas and their Spectra If a picture is worth a thousand words, a spectrum is worth a thousand pictures

Large scale structure

quasars Local structure Cosmic background radiation Primordial nucleosynthesis

Cloudy: Numerical Simulations of Plasmas and their Spectra If a picture is worth a thousand words, a spectrum is worth a thousand pictures

A non-equilibrium gas u Gas emitting spectrum has a very low density u It is exposed to a range of radiation fields and particles u Populations of levels, ionization, spectrum, determined by many micro- physical processes u Not characterized by a single temperature u Or, every level has a different temperature

Photoionization Equilibrium u energetic radiation interacts with surrounding gas –photoionization u photoelectrons heat electron bath u electrons excite heavy elements –collisionally excited line cooling u free electrons recombine –recombination lines

The He-like iso-electronic sequence u He is second most abundant element, produced in Big Bang u A two-electron system, its quantum mechanics is not trivial u Ryan Porter, PhD, in collaboration with Keith MacAdam & Rob Bauman Emission from a pure-helium plasma

Molecular hydrogen u Most baryons are in H 2 u Rotation-vibration emission in IR, electronic absorption in UV u Gargi Shaw, PhD u Energy levels, transition probabilities, well understood u Collisional rates poorly known – being done with ORNL

Heavy-element chemistry u Chemistry in a hard vacuum, at cryogenic temperatures u Series of ion- molecule reactions involving cosmic rays, H 2, and small solids (grains) u Nick Abel, PhD

Cloudy: Numerical Simulations of Plasmas and their Spectra If a picture is worth a thousand words, a spectrum is worth a thousand pictures