Recent observations reveal that, at a given stellar mass, blue galaxies tend to live in haloes with lower mass, while red galaxies live in more massive host haloes. The physical driver behind this is still unclear because theoretical models predict that, at the same halo mass, galaxies with high stellar masses tend to live in early-formed haloes, which naively leads to the opposite trend. Here, we show that the Simba simulation quantitatively reproduces the colour bimodality in the stellar-to-halo mass relation and reveals an inverse relationship between halo formation time and galaxy transition time. It suggests that the origin of this bimodality is rooted in the intrinsic variations of the cold gas content due to halo assembly bias. Simba’s stellar-to-halo mass bimodality quantitatively relies on two aspects of its input physics: (1) jet-mode feedback from active galactic nuclei, which quenches galaxies and sets the qualitative trend, and (2) X-ray feedback from active galactic nuclei, which fully quenches galaxies and yields better agreement with observations. The interplay between the growth of cold gas and the quenching from active galactic nuclei in Simba results in the observed stellar-to-halo mass bimodality.

最近的观测表明，在给定的恒星质量下，蓝色星系往往生活在质量较低的晕圈中，而红色星系则生活在质量更大的宿主晕圈中。这背后的物理驱动因素仍不清楚，因为理论模型预测，在相同的晕质量下，具有高恒星质量的星系往往生活在早期形成的晕中，这天真地导致了相反的趋势。在这里，我们展示了 Simba 模拟定量地再现了恒星与光晕质量关系中的颜色双峰性，并揭示了光晕形成时间和星系转变时间之间的反比关系。这表明这种双峰的起源是由于晕圈组装偏差导致的冷气体含量的内在变化。Simba 的恒星到光晕质量双峰在数量上依赖于其输入物理的两个方面：(1) 来自活动星系核的喷射模式反馈，它使星系猝灭并设定了定性趋势，以及 (2) 来自活动星系核的 X 射线反馈，它完全淬灭了星系并与观测产生了更好的一致性。冷气体的生长和辛巴活跃星系核的淬火之间的相互作用导致了观察到的恒星到光晕的质量双峰。