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| Paper: |
The peak 21-cm surface brightness of spiral galaxies |
| Volume: |
18, The Interpretation of Modern Synthesis Observations of Spiral Galaxies |
| Page: |
163 |
| Authors: |
Dickey, John M. |
| Abstract: |
High-resolution VLA observations of the H I emission from M 31 by Braun (1990) show a very surprising result that the peak brightness temperature of the 21-cm line is consistently higher there than anywhere in the galaxy (175 to 180 K vs 125 to 130 K for the Milky Way). It is suggested that such differences may be common among spiral galaxies, particularly those edge-on enough to have high-velocity gradients along the line of sight, caused simply by a different mixture of the warm and cool phases of H I. From 21-cm absorption observations (Dickey and Brinks, 1988) we know that M 31 has much less cool H I than the Milky Way, but about the same amount of total atomic hydrogen. Using those results, we can explain Braun's numbers with a simple radiative transfer model. |
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