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 a mass range of about five orders of magnitude. Using high-quality spiral-galaxy rotation curves and infrared photometry from the SPARC database, we conduct a systematic study of their central dark matter fraction ($f_{\rm DM}$) calculated within the effective radius and their mass density slope ($\alpha$). 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 at one effective radius. Low-mass ($M_{\rm *} < 10^{10}\, \rm M_{\rm \odot}$) gas-rich spirals span a wide range of $f_{\rm DM}$ values, but their dark matter fractions are systematically lower than in gas-poor systems of similar mass. With increasing galaxy mass, the values of $f_{\rm DM}$ decreases and the mass density profiles steepen. In the most massive late-type gas-poor galaxies, a possible flattening of these trends is noticed. When comparing these results to massive ($M_{\rm *} > 10^{10} M_{\rm \odot}$) early-type galaxies from the SPIDER sample and to dwarf ellipticals from the SMACKED sample, we find that these trends are inverted. Hence, the values of both $f_{\rm DM}$ and $\alpha$, as a function of $M_{\rm *}$, exhibit a U-shape bent. At a fixed stellar mass, the mass density profiles in dwarf ellipticals are steeper than in spirals, which may be the result of 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. These trends with $M_{\rm *}$ can be understood in the context of differential feedback efficiency by supernovae in low-mass galaxies, and by galaxy mergers, AGN feedback or halo mass quenching in higher-mass galaxies....