1996/07/08 by Kenzo Imamura, K. Imamura, Imamura, K. +2
Chemistry · Physics and Astronomy · #Astrophysics (astro-ph) #Astrophysics and Star Formation Studies #Atomic and Molecular Physics #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Molecular Spectroscopy and Structure #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9607044
To appear in A&Ap, Latex 11 pages, 9 figures in 11 ps files
arxiv created 1996/07/08 · openalex publication_date 1996/07/08 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We derive radial and vertical distributions of HI and H2 gas densities in our Galaxy by using the terminal velocity method. We calculate the molecular fraction (fmol) defined as the ratio of the molecular hydrogen to total hydrogen gas density at galactic longitude l= 33 to 64 deg and galactic latitude b=-2 to +2 deg. The thickness of the molecular dominant region fmol > 0.8 is approximately constant (109 +/- 12 pc) at galactocentric distance R = 4.7 to 7.2 kpc. The molecular fraction decreases suddenly at a critical height from the galactic plane, below which the gas disk is almost totally molecular, while it is almost atomic beyond this height. We show that the vertical fmol variation can be reproduced by a model which takes into account the phase transition between HI and H2 gases in the interstellar matter. Key words: Atomic Hydrogen --- the Galaxy --- Interstellar Matter --- Molecular Hydrogen