Spectroscopic decomposition of NGC 3521: unveiling the properties of the
  bulge and disc
  We study the kinematics and the stellar populations of the bulge and disc of
the spiral galaxy NGC 3521. 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 NGC 3521: old ($\geq7$ Gyr), intermediate ($\approx$ 3
Gyr), and young ($\leq$1 Gyr). The mass and light of NGC 3521 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 NGC 3521. 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 sub-solar $\alpha$-enhancement for both the bulge and the disc.
We propose the following picture for the formation of NGC 3521: initial
formation a long time ago ($\geq 7$ Gyr), followed by a second burst of star
formation or a merger ($\approx$ 3 Gyrs ago), which contributed predominantly
to the mass-build up of the bulge. Recently ($\leq 1$ Gyr), the disc of NGC
3521 experienced an additional episode of star formation that started in the
innermost regions.
