Statistics – Computation
Scientific paper
Feb 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...386..120b&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 386, Feb. 10, 1992, p. 120-138.
Statistics
Computation
74
Andromeda Galaxy, Emission Spectra, H Lines, Interstellar Gas, Milky Way Galaxy, Neutral Gases, Absorption Spectra, Computational Astrophysics, Cosmic Dust
Scientific paper
The present study analyzes, in parallel with published data for the Galaxy, neutral hydrogen (H I) absorption and deduced emission detected along seven lines of sight through the disk of M31. It is shown that the brightness temperature of H I emission is coupled to the opacity of the gas. The Galactic relationship shows asymptotic trends at both large and small opacities. A simple yet effective physical model which accounts for this behavior consists of only two independent components: a high-opacity cool component of fixed mean temperature, and a low-opacity warm component of fixed mean brightness. A lower mean gas pressure by a factor of about 2 is argued to be the most plausible mechanism for accounting for a higher cool-component H I temperature in M31. Deduced volume filling factors of the Galactic H I are about 1 and 15 percent, respectively, for the cool and warm components, while for M31 they are 8 and 30 percent. The large ratio of surface to volume filling factors for both cool and warm H I suggests that these components are distributed predominantly as large sheet- or shell-like structures.
Braun Robert
Walterbos Rene A. M.
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