Hyperfine structure emission and absorption lines in hot gas

Syunyaev & Churazov originally pointed out that there is a large set of hyperfine structure lines that are produced by isotopes of the abundant elements. They occur with the H-like (1 electron), Li-like, and Na-like ions by the same process as the hydrogen 21 cm line. Most are highly charged ions, so they will be present in hot X-ray-emitting gas. More recently, Zhang & Sampson computed collision strengths for some of these lines, making it possible to compute accurate level populations, emission, and absorption for the first time. We have incorporated the full set of Syunyaev & Churazov lines into the spectra simulation code Cloudy. We use the Zhang & Sampson calculations as a guide for estimating the order of magnitude of the collision strengths for the lines that do not have collision data. We also calculate a visibility function that predicts which lines will be most easily seen in absorption. The column densities needed to produce strong absorption are greater than those found in even the most massive galaxy clusters, suggesting that these lines will be very hard to detect.