Large scale nested stellar discs in NGC 7217
  NGC7217 is an unbarred early-type spiral galaxy having a multi-segment
exponential light profile and a system of starforming rings of the unknown
origin; it also possesses a circumnuclear gaseous polar disc. We analysed new
long slit spectroscopic data for NGC7217 and derived the radial distributions
of its stellar population parameters and stellar and gaseous kinematics up to
the radius of r~100 arcsec (~8 kpc). We performed the dynamical analysis of the
galaxy by recovering its velocity ellipsoid at different radii, and estimated
the scaleheights of its two exponential discs. The inner exponential stellar
disc of NGC7217 appears to be thin and harbours intermediate age stars (t(SSP)
~ 5 Gyr). The outer stellar disc seen between the radii of 4 and 7 kpc is very
thick (z0 = 1...3 kpc), metal-poor, [Fe/H]<-0.4 dex, and has predominantly
young stars, t(SSP) = 2 Gyr. The remnants of minor mergers of gas-rich
satellites with an early-type giant disc galaxy available in the GalMer
database well resemble different structural components of NGC7217, suggesting
two minor merger events in the past responsible for the formation of the inner
polar gaseous disc and large outer starforming ring. Another possibility to
form the outer ring is the re-accretion of the tidal streams created by the
first minor merger.
