On the nature of 21 CM emission profile structure at high galactic latitude: Implications for the warm neutral medium

Interstellar Neutral Hydrogen Emission Profile Structure

“…The critical ionization velocity is that velocity at which the kinetic energy defined by the relative motion (normal to the local magnetic field) between a plasma and a neutral gas mass permeated by a magnetic field equals the ionization potential of the neutral species. Typical H i profile component line widths appear to cluster in three regimes, as first seen in the data of Verschuur & Schmelz (1989) and specifically discussed by Verschuur & Magnani (1994). The numerical values of these line widths are approximately 6, 13, and 34 km s À1 .…”

“…This study was undertaken in order to determine whether the pattern of line widths reported by Verschuur & Schmelz (1989), Verschuur & Magnani (1994), and subsequently by Verschuur & Peratt (1999) persisted in a large sample of H i profiles judged to be free of sidelobe contamination. It appears that it does, which makes the possible coincidence between the line width families discussed here and critical ionization velocities of the most abundant interstellar atomic species even more intriguing.…”

“…A very faint, broad feature at about À32 km s À1 would not have been included in the line width statistics in this paper. Verschuur & Magnani (1994) and Verschuur & Schmelz (1989). Histograms of line width data were thus prepared in a number of different ways.…”

New Temperatures of Diffuse Interstellar Gas: Thermally Unstable Gas

“…In emission/absorption studies, MWKG decomposed emissionline profiles into Gaussians, with similar results; however, they did not explicitly point out this departure. Verschuur & Magnani (1994) and Heiles (1989) analyzed emission profiles and found numerous components with widths in this range but without absorption data could not conclusively state that the kinetic temperatures were indeed so high.…”

On the Critical Ionization Velocity Effect in Interstellar Space and Possible Detection of Related Continuum Emission

“…What was found is that the low velocity gas surrounding the HI peaks seen in Fig Other data also exist that show that when a broad HI component in a small area of sky is observed with an aperture synthesis telescope the profile structure does indeed reveal the presence of narrower components (colder gas) and that the ensemble velocity distribution accounts for the broader feature observed with lower angular resolution [17].…”