Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988mnras.233..781d&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 233, Aug. 15, 1988, p. 781-790.
Astronomy and Astrophysics
Astronomy
16
Absorption Spectra, Interstellar Matter, Line Spectra, Solar Neighborhood, Spiral Galaxies, Very Large Array (Vla), Hydrogen Atoms, Interstellar Gas, Milky Way Galaxy, Neutral Gases
Scientific paper
The 21-cm absorption through the disk of M31 has been observed, using the VLA to study the cool atomic phase of the interstellar medium in this nearby spiral galaxy. It is found that the abundance of diffuse clouds with tau between 0.125 and 1 in M31 is no higher than in the solar neighborhood of the Milky Way. The mean spin temperature, 300 K, is similar to or higher than the local value. The fraction of the neutral atomic hydrogen in the cool phase is about 0.25 or less. These results imply that M31 has a mixture of warm and cool interstellar phases similar to that in our vicinity of the Milky Way, which suggests either that the heating and cooling balance occurs in a similar pressure environment, or that whatever dynamical processes determine the mixture of warm and cool gas reach a similar equilibrium in M31 as here. Specifically, the warm neutral medium seems to be a robust phase, with a much larger filling-factor than the cool clouds.
Brinks Elias
Dickey John M.
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