Inner polar rings in regular lenticular galaxies

We have investigated a sample of S0 galaxies, mostly with circumnuclear dust lanes orthogonal to their major axes, chosen from Hubble Space Telescope Wide Field Planetary Camera 2 images. Two-dimensional spectroscopy undertaken with the Multipupil Fiber Spectrograph of the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences has revealed that indeed the ionized gas in the centers of these eight lenticular galaxies rotate in the planes nearly orthogonal to the rotation ( and symmetry) planes of their central stellar components. Although almost all the galaxies are located in dense environments, an external origin of this rotation plane tilt is not obvious because all the galaxies but one are known to have extended H I disks, and in two cases where the angular resolution of H I observations allows, we find orthogonality of the external H I and inner ionized gas disks. We discuss a possible relation of the inner gas polar rings to a triaxiality of galactic potential. The stellar populations in the nuclei of all but two galaxies are very old, which excludes recent star formation bursts and proves that the polar orbits of the circumnuclear gas are rather stable. In the nuclei of NGC 2655 and NGC 4111, we have found signatures of star formation bursts some 1.5 - 2 Gyr ago. This finding can be related to very central gas in NGC 2655, which is coplanar to the circumnuclear stellar disk and to radial gas inflow in NGC 4111; just these gas reservoirs and not the polar rings may be responsible for fueling nuclear star formation.