The dichotomy of dark matter fraction and total mass density slope of galaxies over five dex in mass
Résumé
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 (DM) fraction (f_DM) and their mass density slope (α), within their effective radius. We show that lower mass spiral galaxies are more DM dominated and have more shallow mass density slopes when compared with more massive galaxies, which have density profiles closer to isothermal. Low-mass (|${M_{*}}\lesssim 10^{10}\, {\mathrm{M}_\odot}$|) gas-rich spirals span a wide range of f_DM values, but systematically lower than in gas-poor systems of similar mass. With increasing galaxy mass, the values of f_DM 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 (|${M_{*}}\gtrsim 10^{10}\, {\mathrm{M}_\odot}$|) elliptical galaxies from SPIDER and to dwarf ellipticals (dEs) from SMACKED, these trends result to be inverted. Hence, the values of both f_DM and α, as a function of M_*, exhibit a U-shape trend. At a fixed stellar mass, the mass density profiles in dEs 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.