Mathematics – Logic
Scientific paper
Aug 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987apj...319...76s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 319, Aug. 1, 1987, p. 76-83. Research supported by the California Institute
Mathematics
Logic
45
Astronomical Models, Galactic Structure, Hydrogen Atoms, Hydrogen Clouds, Spatial Distribution, Spiral Galaxies, Centimeter Waves, Extragalactic Radio Sources, Galactic Evolution, Interstellar Matter, Milky Way Galaxy
Scientific paper
An interpretation is given for the relatively flat distribution of atomic hydrogen as a function of radius within the visible disks of spiral galaxies and the existence of a correlation between H I surface density and morphological class of spiral galaxy. The H I is mostly contained in constant column density envelopes of molecular clouds. The clouds have a two-dimensional filling factor of unity when a galaxy is viewed face on. The column density of the cloud envelopes depends on the ratio of flux of H2 dissociating radiation in the ambient medium to envelope gas density. The flat H I profiles imply the gas density and pressure follow the ultraviolet ambient flux on kiloparsec scales throughout a given galaxy. Later-type galaxies have larger ultraviolet surface brightnesses, as deduced from the H-alpha surface brightnesses. Therefore, thicker protective H I envelopes develop in late-type spirals.
Federman Steven Robert
Shaya Edward J.
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