The Luminosity Function and stellar Mass to Light ratio of the massive
  globular cluster NGC2419
  We used archival Hubble Space Telescope WFC3 images to obtain the Luminosity
Function of the remote globular cluster NGC2419 from two magnitudes above the
Horizontal Branch level down to \sim3.0 magnitudes below the Turn Off point (to
M_I\sim6.4), approximately covering the range of initial stellar masses 0.5
M_sun<= m <= 0.9 M_sun. The completeness-corrected Luminosity Function does not
display any change of shape over the radial range covered by the WFC3 data, out
to ~6 core radii (r_c), or, equivalently, to ~2 half-light radii. The
Luminosity Function in this radial range is also identical to that obtained
from ground based data at much larger distances from the cluster centre
(12r_c<= R<= 22r_c), in the magnitude range in which the two distributions
overlap (M_I<= 4.0). These results support the conclusion by Dalessandro et al.
that there is no significant mass segregation among cluster stars, hence the
stellar mass-to-light ratio remains constant with distance from the cluster
centre. We fitted the observed Luminosity Function with theoretical
counterparts with the proper age and metallicity from different sets of stellar
evolution models and we consistently derive a total V band mass-to-light ratio
1.2<= M/L_V<= 1.7, by extrapolating to the Hydrogen burning limit, with a
best-fit value M/L_V=1.5 +/- 0.1. On the other hand, assuming that there are no
cluster stars with m<= 0.3 M_sun, we establish a robust lower limit M/L_V> 0.8.
These estimates provide useful constraints for dynamical models of the cluster
that were forced to consider the stellar mass-to-light ratio as a (nearly) free
parameter.
