Dark matter inside early-type galaxies as function of mass and redshift
  We study the behaviour of the dynamical and stellar mass inside the effective
radius (re) of early-type galaxies (ETGs). We use several samples of ETGs
-ranging from 19 000 to 98 000 objects- from the ninth data release of the
Sloan Digital Sky Survey. We consider Newtonian dynamics, different light
profiles and different Initial Mass Functions (IMF) to calculate the dynamical
and stellar mass. We assume that any difference between these two masses is due
to dark matter and/or a non Universal IMF. The main results for galaxies in the
redshift range 0.0024 < z < 0.3500 and in the dynamical mass range 9.5 < log(M)
< 12.5 are: i) A significant part of the intrinsic dispersion of the
distribution of dynamical vs. stellar mass is due to redshift. ii) The
difference between dynamical and stellar mass increases as a function of
dynamical mass and decreases as a function of redshift. iii) The difference
between dynamical and stellar mass goes from approximately 0% to 70% of the
dynamical mass depending on mass and redshift. iv) These differences could be
due to dark matter or a non Universal IMF or a combination of both. v) The
amount of dark matter inside ETGs would be equal to or less than the difference
between dynamical and stellar mass depending on the impact of the IMF on the
stellar mass estimation. vi) The previous results go in the same direction of
some results of the Fundamental Plane (FP) found in the literature in the sense
that they could be interpreted as an increase of dark matter along the FP and a
dependence of the FP on redshift.
