Ubiquitous argonium (ArH${}^{+}$) in the diffuse interstellar medium -- a molecular tracer of almost purely atomic gas

Peter Schilke, David A. Neufeld, Holger S. P. Müller +14

We describe the assignment of a previously unidentified interstellar absorption line to ArH${}^{+}$ and discuss its relevance in the context of hydride absorption in diffuse gas with a…