Twenty-one centimeter line widths of galaxies
The width of the 21-cm velocity profile of a spiral galaxy is an accurate measure of (twice) the Doppler component of its peak rotational velocity. The common and distinctive shape of the profile: steeply sloping edges, two maxima of ''horns,'' and a central minimum, can be accounted for in terms of the gradient of the radial velocity field of the galaxy. Because of this gradient the peak rotational value occurs on the edges of the profile, not at the points of H I signal mxima. The intrinsic line width is correlated with absolute magnitude; as a result line widths, though independent of distance, are subject to the same selection bias as any distance dependent property derived from a magnitude limited sample. This effect is illustrated in the strong correlation between line width and systematic velocity for a sample of 215 galaxies having inclination i > or = 45/sup 0/ and high signal-to-noise ratio in their profiles. For samples of the same absolute magnitude, late-type galaxies have systematically smaller intrinsic line widths than do early-type systems. For a central spherical mass distribution, the average central density in early-type galaxies is significantly higher than that of the latest-type spirals. The use of line widths as distance indicators is subject to uncertainties due to type dependence, Malmquist bias, and the intrinsic scatter inherent in the relation between line width and absolute magnitude. The value of the Hubble constant determined from line widths is similarly subject to both bias and large uncertainty.
- Research Organization:
- National Radio Astronomy Observatory, Green Bank, WV
- OSTI ID:
- 6537889
- Journal Information:
- Astron. J.; (United States), Journal Name: Astron. J.; (United States) Vol. 83:9; ISSN ANJOA
- Country of Publication:
- United States
- Language:
- English
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