What Is Inside Matters: Simulated Green Valley Galaxies Have too Centrally Concentrated Star Formation

In spatially resolved galaxy observations, star formation rate (SFR) radial profiles are found to correlate with total specific SFRs. A central depletion in star formation is thought to correlate with the globally depressed SFRs of, for example, galaxies within the Green Valley (GV). We present, for the first time, radial specific SFR 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 SFR profiles are in reasonable agreement with observations. However, both galaxy samples show centrally concentrated star formation for galaxies in the GV at all galaxy stellar masses, suggesting that quenching occurs from the outside-in, in strong conflict with observations of inside-out quenching. This difference between simulations and observations may be due to resolution issues and/or possible failures in the star formation and feedback implementation in current large-scale cosmological simulations. We conclude that the distribution of star formation within galaxies is a strong additional constraint for simulations and models, in particular, related to the quenching of star formation.