  We present initial results from the "Ponos" zoom-in numerical simulations of
dark matter substructures in massive ellipticals. Two very highly resolved dark
matter halos with $M_{\rm vir}=1.2\times 10^{13}$ $M_{\odot}$ and $M_{\rm
vir}=6.5\times 10^{12}$ $M_{\odot}$ and different ("violent" vs. "quiescent")
assembly histories have been simulated down to $z=0$ in a $\Lambda$CDM
cosmology with a total of 921,651,914 and 408,377,544 particles, respectively.
Within the virial radius, the total mass fraction in self-bound $M_{\rm
sub}>10^6$ $M_{\odot}$ subhalos at the present epoch is 15% for the violent
host and 16.5% for the quiescent one. At $z=0.7$, these fractions increase to
19 and 33%, respectively, as more recently accreted satellites are less prone
to tidal destruction. In projection, the average fraction of surface mass
density in substructure at a distance of $R/R_{\rm vir}=0.02$ ($\sim 5-10$ kpc)
from the two halo centers ranges from 0.6% to $\gtrsim 2$%, significantly
higher than measured in simulations of Milky Way-sized halos. The contribution
of subhalos with $M_{\rm sub} < 10^9$ $M_{\odot}$ to the projected mass
fraction is between one fifth and one third of the total, with the smallest
share found in the quiescent host. We assess the impact of baryonic effects via
twin, lower-resolution hydrodynamical simulations that include
metallicity-dependent gas cooling, star formation, and a
delayed-radiative-cooling scheme for supernova feedback. Baryonic contraction
produces a super-isothermal total density profile and increases the number of
massive subhalos in the inner regions of the main host. The host density
profiles and projected subhalo mass fractions appear to be broadly consistent
with observations of gravitational lenses.
