What Is Inside Matters: Simulated Green Valley Galaxies Have Centrally
  Concentrated Star Formation
  In spatially resolved galaxy observations, star formation rate radial
profiles are found to correlate with total specific star formation rates. A
central depletion in star formation is thought to correlate with the globally
depressed star formation rates of, for example, galaxies within the Green
Valley. We present, for the first time, radial specific star formation rate
profiles for a statistical sample of simulated galaxies from the Illustris and
EAGLE large cosmological simulations. For galaxies on the star-forming
sequence, simulated specific star formation rate profiles are in loose
agreement with observations, although galaxies from the EAGLE simulation are
too centrally peaked, and galaxies from Illustris have a steeper decline at
large radii. However, both galaxy samples show centrally concentrated star
formation for galaxies in the Green Valley at all galaxy stellar masses,
indicating that quenching occurs from the outside-in, in strong conflict with
observations of inside-out quenching. These results appear in spite of the
different feedback models in these two simulations. We conclude that the
distribution of star formation within galaxies is a strong additional
constraint for star formation and feedback models in simulations, in particular
related to the quenching of star formation.
