The association of high-latitude molecular clouds with H I gas

Abstract

view Abstract Citations (43) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Association of High-Latitude Molecular Clouds with H i Gas Gir, Be-Young ; Blitz, Leo ; Magnani, L. Abstract The relationhip between the High Galactic latitude molecular clouds (HCLs) and associated atomic hydrogen gas is investigate. In a global study, we examine a total of 75 HLCs observed in the CO (J=1-0) transition and found that all HCLs are associated with H I gas in both position and velocity with most of the HCLs located along filamentary or looplike H I structures. A small-scale comparison, using Green Bank 43 m H I data toward 10 regions associated with 18 HLCs, shows that the positions of the CO and H I peaks are typically offset from one another by approximately 1.5 deg, comparable to the linear size of the HCLs. No obvious pattern for these CO-H I offsets was found either in relation to the Galactic plane or to an arbitrary explosion center. Typical velocity dispersions of the CO and its associated H I are found to be 0.6 and 3.0 km/s, with a mean H I/CO linewidths ratio of 5.7, which is close to the square root of the ratio of mass of Co/H I possibly indicating energy equipartition between the two phases. The data suggest that the molecular clouds condensed from the atomic gas in situ, rather than having been entrained in the H I. Moreover, the data are consistent with formation from the H I by means of a phase transition in pressure equilibrium. A few cloud complexes are anomalous, perhaps indicating variants in how the clouds formed. We find a minimum total hydrogen column density of 5 x 1020/sq cm and a minimum relative abundance of H2 nucleons of 50% in the 18 clouds we observed. Two of the 10 observed H I clouds, those associated with the molecular clouds MBM 27-29 and MBM 53-55, show clear arclike structures and the latter appear to be expanding with a velocity of about 18 km/s. The kinetic energy of this expanding shell is estimated to be about 4 x 1049 ergs, consistent with having been produced as a result of a supernova explosion or a stellar wind. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174713 Bibcode: 1994ApJ...434..162G Keywords: H I Regions; Interstellar Gas; Milky Way Galaxy; Molecular Clouds; Spatial Distribution; Velocity Distribution; Abundance; Carbon Monoxide; Stellar Winds; Supernovae; Astrophysics; ISM: CLOUDS; ISM: MOLECULES; RADIO LINES: ISM full text sources ADS | data products SIMBAD (18)