A Ring-like Zone of Strong Radial Gas Motions in the Disk of NGC 6181

Abstract

The Sc galaxy NGC 6181 was observed at the 6m telescope of SAO RAS with the scanning Perot-Fabry interferometer in the H-alpha emission line and at the 1m telescope of SAO RAS in BVRI broadband filters with CCD. Subtraction of the mean circular rotation curve from the two-dimensional velocity field has revealed a ring-like zone with a diameter about of 2 kpc where strong radial gas motions are present. The form of the ring is almost perfectly circular in the plane of the galaxy. It is located closer to the center than the beginning of the well-defined spiral structure, but outside of the central bulge-dominated region. The detected radial velocity reduced to the plane of the galaxy is about 100 km/sec and probably is azimuthally dependent. The very inner region of the galaxy, r < 3 arcsec or 0.5 kpc, shows a turn of the dynamical major axis by about 30 deg. Central continuum isophotes are also twisted which suggests the presence of small nuclear bar.