Large-scale nested stellar discs in NGC 7217

NGC 7217 is an unbarred early-type spiral galaxy having a multisegment exponential light profile and a system of star-forming rings of the unknown origin; it also possesses a circum-nuclear gaseous polar disc. We analysed new long-slit spectroscopic data for NGC 7217 and derived the radial distributions of its stellar population parameters, and stellar and gaseous kinematics up to the radius of r approximate to 100 arcsec (similar to 8 kpc). We performed the dynamical analysis of the galaxy by recovering its velocity ellipsoid at different radii and estimated the scale-heights of its two exponential discs. The inner exponential stellar disc of NGC 7217 appears to be thin and harbours intermediate-age stars (t(SSP) approximate to 5 Gyr). The outer stellar disc seen between the radii of 4 and 7 kpc is very thick (z(0) = 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 data base well resemble different structural components of NGC 7217, suggesting two minor merger events in the past responsible for the formation of the inner polar gaseous disc and large outer star-forming ring. Another possibility to form the outer ring is the re-accretion of the tidal streams created by the first minor merger.