HI velocity fields and the shapes of dark matter halos

Details HI velocity fields and the shapes of dark matter halos HI velocity fields and the shapes of dark matter halos

1996-10-08

arxiv.org/abs/astro-ph/9610053v1

Astronomy and Astrophysics

Astrophysics

To appear in "Dark and visible matter in galaxies and cosmological implications", A.S.P. Conf. Series, 8 pages, 3 figures, Lat

Scientific paper

A new method for measuring deviations from axisymmetry in the velocity fields of gas disks is presented. The method is an extension of the method that Franx, van Gorkom and de Zeeuw developed for a single orbit gas ring. The measurement is based upon a higher order harmonic expansion of the full velocity field. Epicyclic theory is used to calculate the effects of a perturbation in the potential on these harmonic terms. It is shown how the s_1 and s_3 harmonics can be used to measure epsilon_R sin(2 phi_{obs}), where epsilon_R is the elongation of the potential and phi_{obs} is an (unknown) viewing angle. As a demonstration, I applied this method to the HI velocity fields of two spiral galaxies, NGC 2403 and NGC 3198.

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