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The stellar kinematics of the spiral galaxies NGC 3198 and NGC 3938

By R. Bottema

Abstract

High resolution spectroscopic long slit observations of the inclined galaxy NGC 3198 and the face-on galaxy NGC 3938 are presented in this paper. From these data radial velocities and stellar velocity dispersions as function of radius have been determined. In NGC 3198 the velocity dispersion in the radial direction is decreasing exponentially with radius, having a scalelength of twice the photometric scalelength and central dispersion of 65+/-10 km s^-1^. If a constant value of Q = 1.7 is assumed (a result from recent numerical experiments), the old disk of NGC 3198 has a constant mass-to-light ratio of 7+/-1.5 (in B). The stellar velocity dispersion in the direction perpendicular to the disk in the case of NGC 3938 is small, between 30-40 km s^-1^ centrally and at one scalelength around 15 km s^-1^. The bulge dispersion is about 40-45 km s^-1^. Assuming that the mass-to-light ratio is constant, its value is ~ 1.1 (old disk, in B). The results concerning the stellar velocity dispersions of 6 late-type spiral galaxies seem to indicate that there is a linear relation between this velocity dispersion and absolute magnitude of these galaxies, in the sense that the dispersion increases when a galaxy is more luminous

Year: 1988
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