Observation of the critical ionization velocity effect in the interstellar medium

Summary form only given. The concept of a critical ionization velocity (CIV) was first introduced by Alfven (1942) as a necessary ingredient of his theory of the formation of the Solar System. As a neutral gas moves through a magnetized plasma, a strong interaction and a rapid ionization of the neutrals takes place if the relative velocity exceeds a certain critical threshold. This "critical velocity" /sup V/c was given by the velocity at which the neutral gas particles with mass M have a kinetic energy equal to their ionization energy /sup eV/i. The observation that the so-called 'clouds' of galactic neutral hydrogen (0.0001 degree of ionization) are actually filamentary in high resolution radiotelescope data led to the discovery that the linewidths of the atomic species in the presence of the self-field of the current-conducting filaments (cosmic z-pinches) fall precisely where predicted by the CIV effect. The H I emission linewidths of the Leiden-Dwingeioo 1996 Survey are figured. Moreover, the infall of neutral gases and their subsequent ionization forces the newly ionized plasma to flow and brake along the magnetic field lines. The subsequent thermalization should then be apparent in the band linewidths at a filament and this is what is observed in the data.