  The colour and metallicity gradients observed in spiral galaxies suggest that
the mass-to-light ratio (M*/L) of the stellar disc is a function of radius.
This is indeed predicted by chemo-photometric models of galactic discs.
  We investigate the distribution of luminous and dark matter in spiral
galaxies, taking into account the radial dependence of the stellar M*/L - which
is usually assumed to be constant in studies of the mass structure.
  From the chemo-photometric models of Portinari et al. (2004) and in agreement
with the observed radial profiles of galaxy colours, we derive the typical
average M*/L profile of the stellar discs of spiral galaxies. We compute the
corresponding Variable Mass-to-Light (VML) stellar surface density profile and
then the VML disc contribution to the circular velocity. We use the latter,
combined with a well studied dark matter velocity profile, to mass model the
co-added rotation curves of Persic et al. (1996). (See
http://www.facebook.com/home.php#!/group.php?gid=310260450630 to retrieve extra
information on the kinematics of galaxies) By investigating rotation curves in
the framework of VML stellar discs, we confirm, to a first approximation, the
scenario obtained with the constant M*/L assumption: a dark matter halo with a
shallow core, an inner baryon-dominated region and a larger proportion of Dark
Matter in smaller objects. However, the resulting size of the the dark halo
core and of the inner baryon dominance region are somewhat smaller. The
stronger role that VML discs have in the innermost regions is important to
constrain the galaxy mass structure in both Lambda Cold Dark Matter and MOND
scenarios.
