Issue |
A&A
Volume 371, Number 2, May IV 2001
|
|
---|---|---|
Page(s) | 538 - 559 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20010392 | |
Published online | 15 May 2001 |
Restoring the full velocity field in the gaseous disk of the spiral galaxy NGC 157
1
Institute of Astronomy of the Russian Academy of Science, 48, Pyatnitskaya St., Moscow 109017, Russia
2
Sternberg Astronomical Institute, Moscow State University, University prospect, 13, Moscow 119899, Russia
3
National Research Center "Troitsk Institute for Innovation and Thermonuclear Researches", Troitsk, Moscow reg. 142092, Russia
4
Special Astrophysical Observatory of the Russian Academy of Sciences, Zelenchukskaya 377140, Russia
5
Observatoire de Marseille, Place le Verrier, 13248 Marseille Cedex 04, France
Corresponding author: A. M. Fridman, afridman@inasan.rssi.ru
Received:
24
August
1999
Accepted:
9
March
2001
This paper is the first in a series of articles devoted to
the construction and analysis of three-component vector velocity
fields in the gaseous disks of spiral galaxies, and to the discovery
of giant anticyclones near corotation which were predicted earlier. We
analyse the line-of-sight velocity field of ionized gas in the spiral
galaxy NGC 157 which has been obtained in the Hα emission line at
the 6 m telescope of SAO RAS. The field contains more than 11 000 velocity
estimates. 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
recently formulated method based on Fourier analysis of the azimuthal
distributions of the line-of-sight velocities at different distances
from the galactic center. To restore the three-component
vector velocity field from the observed line-of-sight velocity
field, two assumptions were made: 1) the perturbed surface density and
residual velocity components can be approximated to the formulae
, where Ci and Fi are respectively
the amplitude and the phase; 2) the perturbed surface
density and residual velocity components satisfy the Euler equations.
The correctness of both assumptions is proven on the basis of the
observational data. 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, as well as the velocity of circular rotation of the disk corrected
for the influence of the velocity perturbations connected with the
spiral arms. Finally, a restoration of the vector velocity field in
the gaseous disk of NGC 157 is performed. 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 any residual velocity field is
predicted. In the reference frame of the spiral pattern, detection of
such cyclones is possible in the galaxies with a radial gradient
of azimuthal residual velocity steeper than that of the rotation
velocity.
Key words: methods: data analysis / galaxies: individual: NGC 157 / galaxies: ISM / galaxies: kinematics and dynamics / galaxies: spiral / galaxies: structure
© ESO, 2001
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