Deep multi-telescope photometry of NGC 5466. II. The radial behaviour of
  the mass function slope
  We use a combination of data acquired with the Advanced Camera for Survey
(ACS) on board the Hubble Space Telescope and the Large Binocular Camera
(LBC-blue) mounted on the Large Binocular Telescope, to sample the main
sequence stars of the globular cluster NGC~5466 in the mass range
$0.3<M/M_\odot<0.8$. We derive the cluster's Luminosity Function in several
radial regions, from the center of the cluster out to the tidal radius. After
corrections for incompleteness and field-contamination, this has been compared
to theoretical Luminosity Functions, obtained by multiplying a simple power law
Mass Function in the form dN/dm$ \propto m^{\alpha}$ by the derivative of the
mass-luminosity relationship of the best-fit isochrone. We find that $\alpha$
varies from -0.6 in the core region to -1.9 in the outer region. This fact
allows us to observationally prove that the stars in NGC 5466 have experienced
the effects of mass segregation. We compare the radial variation of $\alpha$
from the center out to 5 core radii (r$_c$) in NGC 5466 and the globular
cluster M10, finding that the gradient of $\alpha$ in the first 5r$_c$ is more
than a factor of 2 shallower in NGC 5466 than in M10, in line with the
differences in the clusters' relaxation timescales. NGC 5466 is dynamically
younger than M10, with two-body relaxation processes only recently starting to
shape the distribution of main sequence stars. This result fully agrees with
the conclusion obtained in our previous works on the radial distribution of
Blue Straggler Stars, further confirming that this can be used as an efficient
clock to measure the dynamical age of stellar systems.
