Star formation in outer rings of S0 galaxies. II. NGC 4513 -- a
  multi-spin ringed S0 galaxy
  Though S0 galaxies are usually thought to be `red and dead', they demonstrate
often star formation organized in ring structures. We try to clarify the nature
of this phenomenon and its difference from star formation in spiral galaxies.
The moderate-luminosity nearby S0 galaxy, NGC 4513, is studied here. By
applying long-slit spectroscopy along the major axis of NGC 4513, we have
measured gas and star kinematics, Lick indices for the main body of the galaxy,
and strong emission-line flux ratios in the ring. After inspecting the gas
excitation in the ring using the line ratios diagnostic diagrams and have
assured that it is ionized by young stars, we have determined the gas oxygen
abundance by using popular strong-line calibration methods. We have estimated
star formation rate (SFR) in the outer ring by using the archival Galaxy
Evolution Explorer (GALEX) ultraviolet images of the galaxy. The ionized gas
counterrotates the stars over the whole extension of NGC 4513 so being accreted
from outside. The gas metallicity in the ring is slightly subsolar, [O/H]=-0.2
dex, matching the metallicity of the stellar component of the main galactic
disc. However the stellar component of the ring is much more massive than can
be explained by the current star formation level in the ring. We conclude that
probably the ring of NGC 4513 is a result of tidal disruption of a massive
gas-rich satellite, or it may be a consequence of a long star-formation event
provoked by a gas accretion from a cosmological filament having started some 3
Gyr ago.
