  We study the total density distribution in the central regions (~ 1 effective
radius, $R_e$) of early-type galaxies (ETGs), using data from SPIDER and $\rm
ATLAS^{3D}$. Our analysis extends the range of galaxy stellar mass
($M_{\star}$) probed by gravitational lensing, down to ~ $10^{10}\, \rm
M_{\odot}$. We model each galaxy with two components (dark matter halo +
stars), exploring different assumptions for the dark matter (DM) halo profile
(i.e. NFW, NFW-contracted, and Burkert profiles), and leaving stellar
mass-to-light ($M_{\star}/L$) ratios as free fitting parameters to the data.
For all plausible halo models, the best-fitting $M_{\star}/L$, normalized to
that for a Chabrier IMF, increases systematically with galaxy size and mass.
For an NFW profile, the slope of the total mass profile is non-universal,
independently of several ingredients in the modeling (e.g., halo contraction,
anisotropy, and rotation velocity in ETGs). For the most massive ($M_{\star}$ ~
$10^{11.5} \, M_{\odot}$) or largest ($R_{\rm e}$ ~ $15 \, \rm kpc$) ETGs, the
profile is isothermal in the central regions (~$R_{\rm e}/2$), while for the
low-mass ($M_{\star}$ ~ $10^{10.2} \, M_\odot$) or smallest ($R_{\rm e}$ ~ $0.5
\, \rm kpc$) systems, the profile is steeper than isothermal, with slopes
similar to those for a constant-$M/L$ profile. For a steeper concentration-mass
relation than that expected from simulations, the correlation of density slope
with galaxy mass tends to flatten, while correlations with $R_{\rm e}$ and
velocity dispersions are more robust. Our results clearly point to a
"non-homology" in the total mass distribution of ETGs, which simulations of
galaxy formation suggest may be related to a varying role of dissipation with
galaxy mass.
