Dark matter and IMF normalization in Virgo dwarf early-type galaxies

In this work, we analyse the dark matter (DM) fraction, f(DM), and mass-to-light ratio mismatch parameter, delta(IMF) (computed with respect to a Milky Way-like initial mass function), for a sample of 39 dwarf early-type galaxies 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 mass-to-light ratios from the SMAKCED survey. In this first attempt to constrain, simultaneously, the initial mass function (IMF) normalization and the DM content, we explore the impact of different assumptions on the DM model profile. On average, for an Navarro, Frenk & White (NFW) profile, the dIMF is consistent with a Chabrier-like normalization (delta(IMF) similar to 1), with f(DM) similar to 0.35. One of the main results of this work is that for at least a few systems the dIMF are heavier than the Milky Way-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) (less than or similar to 1) and larger f(DM). A constant M/L profile with null f(DM) gives the heaviest delta(IMF) (similar to 2). In the MONDian framework, we find consistent results to those for our reference NFW model. If confirmed, the large scatter of dIMF 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) (similar to 100 kms(-1)) early-type galaxies (ETGs). Furthermore, we find f(DM) consistent with values from the SMAKCED survey, and find a double-value behaviour of f(DM) with stellar mass, which mirrors the trend of dynamical M/L and global star formation efficiency (from abundance matching estimates) with mass.