Galaxy bimodality due to cold flows and shock heating

We address the origin of the robust bimodality observed in galaxy properties about a characteristic stellar mass ∼3 × 1010 M⊙. Less massive galaxies tend to be ungrouped blue star forming discs, while more massive galaxies are typically grouped red old-star spheroids. Colour–magnitude data show a gap between the red and blue sequences, extremely red luminous galaxies already at z∼ 1, a truncation of today's blue sequence above L*, and massive starbursts at z∼ 2–4. We propose that these features are driven by the thermal properties of the inflowing gas and their interplay with the clustering and feedback processes, all functions of the dark matter halo mass and associated with a similar characteristic scale. In…