Back to Volume
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.
Back to Volume