The dichotomy of dark matter fraction and total mass density slope of
  galaxies over five dex in mass
  We analyse the mass density distribution in the centres of galaxies across
five orders of magnitude in mass range. Using high-quality spiral galaxy
rotation curves and infrared photometry from SPARC, we conduct a systematic
study of their central dark matter fraction ($f_{\rm DM}$) and their mass
density slope ($\alpha$), within their effective radius. We show that
lower-mass spiral galaxies are more dark matter dominated and have more shallow
mass density slopes when compared with more massive galaxies, which have
density profiles closer to isothermal. Low-mass ($M_{\star} \lesssim 10^{10}\,
\rm M_{\odot}$) gas-rich spirals span a wide range of \fdm\ values, but
systematically lower than in gas-poor systems of similar mass. With increasing
galaxy mass, the values of \fdm\ decrease and the density profiles steepen. In
the most massive late-type gas-poor galaxies, a possible flattening of these
trends is observed. When comparing these results to massive ($M_{\star} \gtrsim
10^{10}M_{\odot}$) elliptical galaxies from SPIDER and to dwarf ellipticals
from SMACKED, these trends result to be inverted. Hence, the values of both
$f_{\rm DM}$ and $\alpha$, as a function of $M_{\star}$, exhibit a U-shape
trend. At a fixed stellar mass, the mass density profiles in dwarf ellipticals
are steeper than in spirals. These trends can be understood by stellar feedback
from a more prolonged star formation period in spirals, causing a
transformation of the initial steep density cusp to a more shallow profile via
differential feedback efficiency by supernovae, and by galaxy mergers or AGN
feedback in higher-mass galaxies.
