ALBERT

Description: We study the total density distribution in the central regions (1 effective radius, R e ) of early-type galaxies (ETGs), using data from SPIDER and ATLAS 3D . Our analysis extends the range of galaxy stellar mass ( M * ) probed by gravitational lensing, down to ~ 10 10 M . We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter halo profile (i.e. NFW, NFW-contracted, and Burkert profiles), and leaving stellar mass-to-light ( M * / L ) ratios as free fitting parameters to the data. For all plausible halo models, the best-fitting M * / L , normalized to that for a Chabrier initial mass function, increases systematically with galaxy size and mass. For an NFW profile, the slope of the total mass profile is non-universal, independently of several ingredients in the modelling (e.g. halo contraction, anisotropy, and rotation velocity in ETGs). For the most massive ( M *  ~ 10 11.5 M ) or largest ( R e ~ 15 kpc) ETGs, the profile is isothermal in the central regions (~ R e /2), while for the low-mass ( M *  ~ 10 10.2 M ) or smallest ( R e ~ 0.5 kpc) systems, the profile is steeper than isothermal, with slopes similar to those for a constant- M / L profile. For a steeper concentration–mass relation than that expected from simulations, the correlation of density slope with galaxy mass tends to flatten, while correlations with R e and velocity dispersions are more robust. Our results clearly point to a ‘non-homology’ in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.