The failure of stellar feedback, magnetic fields, conduction, and
  morphological quenching in maintaining red galaxies
  The quenching "maintenance'" and related "cooling flow" problems are
important in galaxies from Milky Way mass through clusters. We investigate this
in halos with masses $\sim 10^{12}-10^{14}\,{\rm M}_{\odot}$, using
non-cosmological high-resolution hydrodynamic simulations with the FIRE-2
(Feedback In Realistic Environments) stellar feedback model. We specifically
focus on physics present without AGN, and show that various proposed "non-AGN"
solution mechanisms in the literature, including Type Ia supernovae, shocked
AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fields,
Spitzer-Braginskii conduction, or "morphological quenching" do not halt or
substantially reduce cooling flows nor maintain "quenched" galaxies in this
mass range. We show that stellar feedback (including cosmic rays from SNe)
alters the balance of cold/warm gas and the rate at which the cooled gas within
the galaxy turns into stars, but not the net baryonic inflow. If anything,
outflowing metals and dense gas promote additional cooling. Conduction is
important only in the most massive halos, as expected, but even at $\sim
10^{14}\,{\rm M}_{\odot}$ reduces inflow only by a factor $\sim 2$ (owing to
saturation effects and anisotropic suppression). Changing the morphology of the
galaxies only slightly alters their Toomre-$Q$ parameter, and has no effect on
cooling (as expected), so has essentially no effect on cooling flows or
maintaining quenching. This all supports the idea that additional physics,
e.g., AGN feedback, must be important in massive galaxies.
