Revisiting the Bulge-Halo Conspiracy. I. Dependence on Galaxy Properties and Halo Mass

We carry out a systematic investigation of the total mass density profile of massive (log M-star/M-circle dot greater than or similar to 11.3) early-type galaxies and its dependence on galactic properties and host halo mass with the aid of a variety of lensing/dynamical data and large mock galaxy catalogs. The latter are produced via semi-empirical models that, by design, are based on just a few basic input assumptions. Galaxies with measured stellar masses, effective radii, and Sersic indices, are assigned, via abundance matching relations, host dark matter halos characterized by a typical ACDM profile. Our main results are as follows. (1) In line with observational evidence, our semi-empirical models naturally predict that the total, mass-weighted density slope at the effective radius gamma' is not universal, steepening for more compact and/or massive galaxies, but flattening with increasing host halo mass. (2) Models characterized by a Salpeter or variable initial mass function (IMF) and uncontracted dark matter profiles are in good agreement with the data, while a Chabrier IlVIF and/or adiabatic contractions/expansions of the dark matter Mstar highly disfavored. (3) Currently available data on the mass density profiles of very massive galaxies (log M-star/M-circle dot greater than or similar to 12), with M-halo greater than or similar to 3 x 10(14) M-circle dot, favor instead models with a stellar profile flatter than a Sersic one in the very inner regions (r less than or similar to 3-5 kpc), and a cored NFW or Einasto dark matter profile with median halo concentration a factor of similar to 2 or less than or similar to 1.3, respectively, higher than those typically predicted by N -body numerical simulations.