  We present a systematic study of ground state and spectroscopic properties of
many-electron nanoscopic quantum rings. Addition energies at zero magnetic
field (B) and electro-chemical potentials as a function of $B$ are given for a
ring hosting up to 24 electrons. We find discontinuities in the excitation
energies of multipole spin and charge density modes, and a coupling between the
charge and spin density responses that allow to identify the formation of
ferromagnetic ground states in narrow magnetic field regions. These effects can
be observed in Raman experiments, and are related to the fractional
Aharonov-Bohm oscillations of the energy and of the persistent current in the
ring.
