  The condensation of baryons within a dark matter (DM) halo during galaxy
formation should result in some contraction of the halo as the combined system
settles into equilibrium. We quantify this effect on the cuspy primordial halos
predicted by DM-only simulations for the baryon distributions observed in the
galaxies of the SPARC database. We find that the DM halos of high surface
brightness galaxies (with $\Sigma_{\rm eff}\gtrsim100$ $L_\odot$ pc$^{-2}$ at
3.6 $\mu$m) experience strong contraction. Halos become more cuspy as a result
of compression: the inner DM density slope increases with the baryonic surface
mass density. We iteratively fit rotation curves to find the balance between
initial halo parameters (constrained by abundance matching), compression, and
stellar mass-to-light ratio. The resulting fits often require lower stellar
masses than expected for stellar populations, particularly in galaxies with
bulges: stellar mass must be reduced to make room for the DM it compresses.
This trade off between dark and luminous mass is reminiscent of the cusp-core
problem in dwarf galaxies, but occurs in more massive systems: the
present-epoch DM halos cannot follow from cuspy primordial halos unless (1) the
stellar mass-to-light ratios are systematically smaller than expected from
standard stellar population synthesis models, and/or (2) there is a net outward
mass redistribution from the initial cusp, even in massive galaxies widely
considered to be immune from such effects.
