Photoionization and electron-ion recombination in astrophysical plasmas

Photoionization and its inverse, electron-ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyse the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. We highlight how the data needed for spectral analyses, and the required accuracy, varies considerably in different astrophysical environments. We then discuss photoionization processes, highlighting resonances in their cross-sections. Next we discuss radiative recombination, and low and high temperature dielectronic recombination. The possible suppression of low temperature dielectronic recombination (LTDR) and high temperature dielectronic recombination (HTDR) due to the radiation field and high densities is discussed. Finally we discuss a few astrophysical examples to highlight photoionization and recombination processes.
Comment: 25 pages, 15 figures, review article. To be published in a special issue of Atoms (ISSN 2218-2004): "Photoionization of Atoms" eds. S. N. Nahar, G. Hinojosa Version 2: Corrected typo in equation 5 (thanks to Stan Owocki for pointing this out)