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Paper: AU Scale Structures in Extra-planar Gas
Volume: 331, Extra-Planar Gas
Page: 41
Authors: Richter, P.
Abstract: Recent spectroscopic observations of intermediate- and high-velocity clouds (IVCs and HVCs) in the Milky Way halo have unveiled the presence of diffuse interstellar molecular hydrogen (H2) several kpc away from the Galactic disk. Most of this H2 gas appears to reside in relatively small (~ 0.1 pc), dense (nH ≈ 30 cm−3) gaseous filaments that probably are part of the cold neutral medium (CNM) in IVCs and HVCs. Also much smaller structures at AU scale and very high densities (nH ≈ 800 cm−3) have been observed, suggesting the presence of tiny-scale atomic structures (TSAS) in the Milky Way's extra-planar gas. It is not yet understood how such objects can form and exist in the Milky Way halo, but the high detection rate of H2 absorption in IVCs implies that the CNM represents a gas phase that is characteristic for neutral clouds in the lower halo.
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