Booklet "Institute of Astronomy RAS", Moscow, 1996, pp.22-24.

Prediction and discovery of new structures in spiral galaxies: giant anticyclones.

On the base of laboratory simulations (on rotating shallow water) of the formation of spiral arms in galactic gaseous disks, the existence of giant anticyclones in them was predicted. Numerical simulations shown that the vortex structures arise on a linear stage of spiral arms formation simultaneously with the latter.

Line-of-sight velocity fields of gaseous clouds in galactic disks of NGC 157 and NGC 6181 observed at the 6-meter telescope SAO RAS (Russia) were analyzed by the new method of reconstruction of 3D vector velocity field --- three components of velocities. The analysis leads to the discovery of giant anticyclons in NGC 157 (overlaid on H_alpha image) and NGC 6181. Locations of anticyclone centers and its sizes fit the analytical theory, the laboratory simulations on the rotating shallow water and numerical simulations.

The velocity field model of gaseous clouds combined the circular rotation and motion in spiral arms in the solar vicinity was first built. Some parameters of the model were determined from observations and it is shown that the model describes all main peculiarities of the observed velocity field. It has strengthened the hypothesis by Fridman on the possible existences of anticyclones at a galactocentric radius of the Sun.

Thus second giants structures, after spiral arms, in spiral galactic disks are discovered. In spite of the fact that the spiral structures are investigated intensively during more than one century the discovered vortex structures give much more information in understanding dynamical processes in galaxies. In particular, the vortex positions relative to the spiral arms jointly with the observed rotation curve can serve as a test for determining the nature of a spiral-vortex structure generation.

This work was supported by Russian Foundation for Basic Research (grants 93-02-17248, 96-02-17792).

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