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Up: A ring-like zone

1. Introduction

NGC 6181 is an isolated late-type giant spiral galaxy whose high surface brightness of gas emission and inclination of about tex2html_wrap_inline1391 are favorable for a detailed kinematical study. Global parameters of the galaxy are listed in Table 1 (click here) being taken basically from LEDA (Lyon-Meudon Extragalactic Database). The first kinematical investigation of NGC 6181 was undertaken nearly 30 years ago by Burbidge et al. (1965). They obtained three spectral long-slit cross-sections of the galaxy and found line-of-sight velocity distributions to be quite asymmetrical. They concluded that NGC 6181 is not an axisymmetric galaxy being intermediate between a barred and a normal spiral. The form of thin dust lanes in the center of NGC 6181 gave some support to this hypothesis. In addition, they noted that ``the structural center of the galaxy is not the center of the velocity distribution", because the systemic velocities determined from the outer and the inner parts of line-of-sight velocity curves disagreed.

Our group (Afanasiev et al. 1992) has repeated a long-slit kinematical study of NGC 6181 at the 6m telescope of the Special Astrophysical Observatory (SAO RAN) and fully confirmed the unusual asymmetrical character of the one-dimensional line-of-sight velocity distributions. It has been proposed that it is the southern part of the galaxy which reveals strong non-circular gas motions up to distances of about 20tex2html_wrap1419 from the center. But it became evident that the obtaining of the two-dimensional velocity field is necessary to clarify the situation.

Table 1: Global parameters of NGC 6181

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