Interstellar Matters: Neutral Hydrogen and the Galactic Magnetic Field

• Published in: The Astrophysical journal 2018-11, Vol.867 (2), p.139
• Main Authors: Verschuur, G. L., Schmelz, J. T., Asgari-Targhi, M.
• Format: Article
• Language: English
• Subjects: Astrophysics; Declination; Hydrogen; Interstellar magnetic fields; ISM: atoms; ISM: clouds; ISM: magnetic fields; Magnetic fields; Morphology; Substructures; Velocity
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aae4df

A very long and nearly straight H i filament at about −60 km s−1 in the southern Galactic hemisphere, seen nearly normal to the line of sight and well separated from low-velocity gas, has been studied in several ways in order to understand its physics, structure, and morphology. Gaussian analysis of 1800 profiles and examination of 140 declination-velocity cross sections shows that an underlying H i component, which is at least 15° long and about 1° wide, has a typical line width of 21 km s−1. It does not appear to be in thermal pressure equilibrium with its surroundings; rather, it may be confined by a magnetic field of 18 G. Narrow, elongated features (threads), probably unresolved in the 4′ H i observations, have been identified within the boundaries of the filament. In general, each of these threads has two emission components, with line widths of the order of 8 and 3 km s−1, which may wind around each other. Analysis suggests that these cooler components have an average density of 29 cm−3 and may be confined by a magnetic field of 5 G. These results, taken together, can be explained if this southern filament has magnetic substructure.