On the physical origins for the two-halo conformity

The two-halo conformity is that if a central galaxy in a dark matter halo is quenched in star formation, the central galaxies in other neighboring halos (within ~ 4 Mpc) even with no causal contact seem conformed to be quenched. The galactic similarity ranging far beyond the virial radius of each dark matter halo cannot be explained by known environmental effects (ram pressure, tidal interaction, etc.). Here, using a cosmological hydrodynamic simulation, we put forward new physical origins for the phenomenon; the back-splash galaxies scenario and the halo assembly bias scenario. We discuss the relative importance of the two explanations on a quantitative basis.