Restoring the full velocity field in the gaseous disk ofthe spiral galaxy NGC 157

Details Restoring the full velocity field in the gaseous disk ofthe spiral galaxy NGC 157 Restoring the full velocity field in the gaseous disk ofthe spiral galaxy NGC 157

2001-03-30

arxiv.org/abs/astro-ph/0103507v1

Astronomy and Astrophysics

Astrophysics

23 pages including 25 eps-figures. Accepted for publication in A&A

Scientific paper

10.1051/0004-6361:20010392

We analyse the line-of-sight velocity field of ionized gas in the spiral galaxy NGC 157 which has been obtained in the H\alpha emission at the 6m telescope of SAO RAS. The existence of systematic deviations of the observed gas velocities from pure circular motion is shown. A detailed investigation of these deviations is undertaken by applying a Fourier analysis of the azimuthal distributions of the line-of-sight velocities at different distances from the galactic center. As a result of the analysis, all the main parameters of the wave spiral pattern are determined: the corotation radius, the amplitudes and phases of the gas velocity perturbations at different radii, and the velocity of circular rotation of the disk corrected for the velocity perturbations due to spiral arms. At a high confidence level, the presence of the two giant anticyclones in the reference frame rotating with the spiral pattern is shown; their sizes and the localization of their centers are consistent with the results of the analytic theory and of numerical simulations. Besides the anticyclones, the existence of cyclones in residual velocity fields of spiral galaxies is predicted. In the reference frame rotating with the spiral pattern these cyclones have to reveal themselves in galaxies where a radial gradient of azimuthal residual velocity is steeper than that of the rotation velocity (abridged).

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