The response of dark matter haloes to elliptical galaxy formation: a new
  test for quenching scenarios
  We use cosmological hydrodynamical zoom-in simulations with the SPH code
gasoline of four haloes of mass M_{200} \sim 10^{13}\Msun to study the response
of the dark matter to elliptical galaxy formation. Our simulations include
metallicity dependent gas cooling, star formation, and feedback from massive
stars and supernovae, but not active galactic nuclei (AGN). At z=2 the
progenitor galaxies have stellar to halo mass ratios consistent with halo
abundance matching, assuming a Salpeter initial mass function. However by z=0
the standard runs suffer from the well known overcooling problem,
overpredicting the stellar masses by a factor of > 4. To mimic a suppressive
halo quenching scenario, in our forced quenching (FQ) simulations, cooling and
star formation are switched off at z=2. The resulting z=0 galaxies have stellar
masses, sizes and circular velocities close to what is observed. Relative to
the control simulations, the dark matter haloes in the FQ simulations have
contracted, with central dark matter density slopes d\log\rho/d\log r \sim
-1.5, showing that dry merging alone is unable to fully reverse the contraction
that occurs at z>2. Simulations in the literature with AGN feedback however,
have found expansion or no net change in the dark matter halo. Thus the
response of the dark matter halo to galaxy formation may provide a new test to
distinguish between ejective and suppressive quenching mechanisms.
