Further evidence for the critical ionization velocity signature in interstellar neutral hydrogen emission profiles

摘要

Summary form only given. In previous studies it was found that interstellar neutral hydrogen (HI) emission spectra manifest several families of linewidths whose numerical values may be related to the critical ionization velocities (CIVs) of the most abundant interstellar atomic species. Three families of linewidths are prominent: 34 km/s, corresponding to the CIV for helium, 13 km/s, corresponding to the CIVs of carbon, nitrogen and oxygen, and 6 km/s, corresponding to the CIVs of heavy HI "metals" such as Mg, Al, Fe, Na and Ca. Extended new analysis of HI emission profiles has produced data on over 15,000 Gaussian components. The results, which pertain to local HI, within a few 100 pc of the Sun, show that these families of linewidths are pervasive, but not uniform. The extent to which the HI gas exhibits large-scale, velocity disturbances alters the relative presence of the various components. The new study also found a linewidth signature that may be due to a 10,000 K plasma interacting with the neutral gas in some directions on the sky. The mechanism by which the CIV effect operates in interstellar space remains to be demonstrated. However, it is significant that the helium CIV signature producing the 34 km/s wide family of emission profiles may also be recognized in numerous studies published by others over the last 30 years, include HI studies of the Magellanic stream, very high-velocity clouds and the so-called compact high-velocity clouds, all of which are believed to be intergalactic