  We present an analysis of the metallicity distribution functions of fields
projected along the minor axis for a sample of inclined spiral galaxies in
order to search for evidence of the presence of multiple stellar populations.
In all cases, the stellar populations appear to have asymmetric metallicity
distributions with very high confidence levels. The mean metallicities of both
stellar subpopulations, determined from mixture modelling of the metallicity
distribution functions, correlate with parent galaxy luminosity. This suggests
that the vast majority of field stars have probably formed in galactic
fragments that were already embedded in the dark matter halo of the final
galaxy. The steeper correlation between the mean stellar metallicity and parent
galaxy luminosity is driven by an increasing fraction of metal-rich stars with
increasing galaxy luminosity. Metal-poor components show larger dispersion in
metallicity than metal-rich components. These properties are in striking
similarity with those of globular cluster subpopulations around early-type
galaxies. The properties of field stars along the minor axis are consistent
with a formation scenario in which the metal-poor stars formed in all galaxies,
possibly as a result of tidal disruption of dwarf-like objects. An additional
metal-rich component might be related to the formation of the bulge and/or the
disk.
