Velocity dispersions in the bulges of spiral galaxies

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Galactic Nuclei, Galactic Structure, Spiral Galaxies, Velocity Distribution, Astronomical Spectroscopy, Elliptical Galaxies, Luminous Intensity, Optical Emission Spectroscopy

Scientific paper

Velocity dispersions have been obtained in the central regions of 30 galaxies, 21 of which are spirals. Spectra were obtained at McGraw-Hill Observatory with an intensified Reticon scanner. A 'Fourier quotient' technique was used to yield dispersions, with typical uncertainties in the central velocity dispersions of 22 km/s. It is found that the spheroidal bulges of spiral galaxies obey the same L equals sigma to the 4th relation between luminosity and velocity dispersion that has been found in ellipticals, but with dispersions smaller by 15% at a given absolute magnitude. This may be understood as a difference in mass-to-light ratio, a difference in rotational support, or a difference in central surface brightness. The bulge dispersions are compared with neutral hydrogen velocity widths and it is found that if most of the mass of spiral galaxies is in a dark isothermal component, the bulge is somewhat cooler than this halo.

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