A. M. Fridman

The orientation parameters and rotation curves of 15 spiral galaxies

We analyzed ionized gas motion and disk orientation parameters for 15 spiral galaxies. Their velocity fields were measured with the Ha emission line by using the Fabry-Perot interferometer at the 6 m telescope of SAO RAS. Special attention is paid to the problem of estimating the position angle of the major axis (PA 0 ) and the inclination (i) of a disk, which strongly affect the derived circular rotation velocity. We discuss and compare different methods of obtaining these parameters from kinematic and photometric observations, taking into account the presence of regular velocity (brightness) perturbations caused by spiral density waves. It is shown that the commonly used method of tilted rings may lead to systematic errors in the estimation of orientation parameters (and hence of circular velocity) being applied to galaxies with an ordered spiral structure. Instead we recommend using an assumption of constancy of i and PA 0 along a radius, to estimate these parameters. For each galaxy of our sample we present monochromatic He- and continuum maps, velocity fields of ionized gas, and the mean rotation curves in the frame of a model of pure circular gas motion. Significant deviations from circular motion with amplitudes of several tens of km s -1 (or higher) are found in almost all galaxies. The character and possible nature of the non-circular motion are briefly discussed.

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

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).

Giant cyclones in gaseous discs of spiral galaxies

Abstract We report the detection of giant cyclonic vortices in the gaseous disc of the spiral galaxy NGC 3631 in the reference frame rotating with the spiral pattern. A presence of such structures was predicted by the authors for galaxies, where the radial gradient of the perturbed velocity exceeds that of the rotational velocity. This situation really takes place in NGC 3631.

Are there Giant Vortices near Solar Circle

The analysis of the observational line-of-sight radial velocity field of molecular clouds, connecting with young stars, has strengthened the Fridman’s hypothesis (1994) on the possible existence of anticyclone in the solar neighborhood. Anticyclones are located near corotation radius of the observed spiral arms, a number of which is equal to a number of vortices. Our calculations show that the four-vortices model fits observational data fairly well.