  We introduce a mass dependent density profile to describe the distribution of
dark matter within galaxies, which takes into account the stellar-to-halo mass
dependence of the response of dark matter to baryonic processes. The study is
based on the analysis of hydrodynamically simulated galaxies from dwarf to
Milky Way mass, drawn from the MaGICC project, which have been shown to match a
wide range of disk scaling relationships. We find that the best fit parameters
of a generic double power-law density profile vary in a systematic manner that
depends on the stellar-to-halo mass ratio of each galaxy. Thus, the quantity
Mstar/Mhalo constrains the inner ($\gamma$) and outer ($\beta$) slopes of dark
matter density, and the sharpness of transition between the slopes($\alpha$),
reducing the number of free parameters of the model to two. Due to the tight
relation between stellar mass and halo mass, either of these quantities is
sufficient to describe the dark matter halo profile including the effects of
baryons. The concentration of the haloes in the hydrodynamical simulations is
consistent with N-body expectations up to Milky Way mass galaxies, at which
mass the haloes become twice as concentrated as compared with pure dark matter
runs. This mass dependent density profile can be directly applied to rotation
curve data of observed galaxies and to semi analytic galaxy formation models as
a significant improvement over the commonly used NFW profile.
