Tiny-Scale Atomic Structure and the Cold Neutral Medium--Review and Recap

Abstract

Almost a decade ago I wrote an article with the same title as this. It focused on the physical properties of the Tiny-Scale Atomic Structure (TSAS) as discrete structures of the Cold Neutral Medium (CNM). To be observable, tiny discrete structures that don't grossly violate pressure equilibrium need two attributes: low temperatures and geometrical anisotropy. Here I update that article. I discuss thermal and pressure equilibrium, ionization, optical lines, H_2 abundance, and evaporation.