The Gas Kinematics, Excitation, and Chemistry, in Connection with Star Formation, in Lenticular Galaxies

We present long-slit and panoramic spectroscopy of extended gaseous disks in 18 S0 galaxies, mostly in groups. The gas has often decoupled kinematics: at least five galaxies demonstrate strongly inclined large-scale ionized gas disks, seven galaxies reveal circumnuclear polar disks, and in NGC 2551 the ionized gas, although confined to the main plane, counterrotates the stars. The gas excitation analysis reveals ionization by young stars in 12 of 18 S0 galaxies; current star formation in these galaxies is confined to ring-like zones coinciding with their UV rings. Gas oxygen abundances in the rings are around 0.7 Z _⊙ and correlate neither with the ring radius nor with the metallicity of the stellar population. By applying tilted ring analysis to the velocity fields, we have traced the gas rotation plane lines of nodes along the radius. We find that current star formation proceeds usually where the gas lies strictly in the stellar disk planes and rotates circularly; the sense of the gas rotation does not matter (the counterrotating gas in NGC 2551 forms stars). In the galaxies without current star formation the extended gaseous disks either are in steady-state quasi-polar orientation or were acquired recently through the misaligned external filaments provoking shock-like excitation. Our data imply a crucial difference of the accretion regime in S0s with respect to spirals: the geometry of gas accretion in S0s is typically off-plane.