Abstract

We study the kinematics and the stellar populations of the bulge and disc of the spiral galaxy NGC3521. At each position in the field of view, we separate the contributions of the bulge and the disc from the total observed spectrum and study their kinematics, age, and metallicities independently. Their properties are clearly distinct: the bulge rotates more slowly, has a higher velocity dispersion, and is less luminous than the disc. We identify three main populations of stars in NGC3521: old (>= 7Gyr), intermediate (approximate to 3 Gyr), and young (= 1Gyr). The mass and light of NGC3521 are dominated by the intermediate stellar population. The youngest population contributes mostly to the disc component and its contribution increases with radius. We also study the luminosity-weighed properties of the stars in NGC3521. Along the photometric major axis, we find (i) no age gradient for the stars in the bulge, and a negative age gradient for the stars in the disc; (ii) negative metallicity gradients and subsolar alpha-enhancement for both the bulge and the disc. We propose the following picture for the formation of NGC3521: initial formation a long time ago (>= 7Gyr), followed by a second burst of star formation or a merger (approximate to 3Gyr ago), which contributed predominantly to the mass build-up of the bulge. Recently (= 1 Gyr), the disc of NGC3521 experienced an additional episode of star formation that started in the innermost regions.