Dark Matter and IMF normalization in Virgo dwarf early-type galaxies
  In this work we analyze the dark matter (DM) fraction, $f_{DM}$, and
mass-to-light ratio mismatch parameter, $\delta_{IMF}$ (computed with respect
to a Milky-Way-like IMF), for a sample of 39 dwarf early-type galaxies (dEs) in
the Virgo cluster. Both $f_{DM}$ and $\delta_{IMF}$ are estimated within the
central (one effective radius) galaxy regions, with a Jeans dynamical analysis
that relies on galaxy velocity dispersions, structural parameters, and stellar
M/L ratios from the SMAKCED survey. In this first attempt to constrain,
simultaneously, the IMF normalization and the DM content, we explore the impact
of different assumptions on the DM model profile. On average, for a NFW
profile, the $\delta_{IMF}$ is consistent with a Chabrier-like normalization
($\delta_{IMF} \sim 1$), with $f_{DM} \sim 0.35$. One of the main results of
the present work is that for at least a few systems the $\delta_{IMF}$ is
heavier than the MW-like value (i.e. either top- or bottom-heavy). When
introducing tangential anisotropy, larger $\delta_{IMF}$ and smaller $f_{DM}$
are derived. Adopting a steeper concentration-mass relation than that from
simulations, we find lower $\delta_{IMF}$ ($< 1$) and larger $f_{DM}$. A
constant M/L profile with null $f_{DM}$ gives the heaviest $\delta_{IMF}$
($\sim 2$). In the MONDian framework, we find consistent results to those for
our reference NFW model. If confirmed, the large scatter of $\delta_{IMF}$ for
dEs would provide (further) evidence for a non-universal IMF in early-type
systems. On average, our reference $f_{DM}$ estimates are consistent with those
found for low-$\sigma_{e}$ ($\rm \sim 100 \, \rm km s^{-1}$) early-type
galaxies (ETGs). Furthermore, we find $f_{DM}$ consistent with values from the
SMAKCED survey, and find a double-value behavior of $f_{DM}$ with stellar mass,
which mirrors the trend of dynamical M/L and global star formation efficiency
with mass.
