On the Origin of the Hubble Sequence: I. Insights on Galaxy Color Migration from Cosmological Simulations

An analysis of more than 3000 galaxies resolved at better than 114 pc/h at z = 0.62 in a “LAOZI ” cosmological adaptive mesh refinement hydrodynamic simulation is performed and insights gained on star formation quenching and color migration. The vast majority of red galaxies are found to be within three virial radii of a larger galaxy, at the onset of quenching when the specific star formation rate experiences the sharpest decline to fall below ∼ 10−2−10−1Gyr−1 (depending on the redshift). We shall thus call this mechanism “environment quenching”, which encompasses satellite quenching. Two physical processes are largely responsible: ram-pressure stripping first disconnects the galaxy from the cold gas supply on large scales, followed by a longer period of cold gas starvation taking place in high velocity dispersion environment, during the early part of which the existing dense cold gas in the central region ( ≤ 10kpc) is consumed by in situ star formation. Quenching is found to be more efficient (i.e., a larger fraction of galaxies being quenched), but not faster (i.e., duration being weakly dependent on environment), on average, in denser environment. Throughout this quenching perio