The formation of massive, quiescent galaxies at cosmic noon

The cosmic noon (z ~ 1.5-3) marked a period of vigorous star formation for most galaxies. However, about a third of the more massive galaxies at those times were quiescent in the sense that their observed stellar populations are inconsistent with rapid star formation. The reduced star formation activity is often attributed to gaseous outflows driven by feedback from supermassive black holes, but the impact of black hole feedback on galaxies in the young Universe is not yet definitively established. We analyse the origin of quiescent galaxies with the help of ultrahigh resolution, cosmological simulations that include feedback from stars but do not model the uncertain consequences of black hole feedback. We show that dark matter haloes with specific accretion rates below ~0.25-0.4 Gyr^-1 preferentially host galaxies with reduced star formation rates and red broad-band colours. The fraction of such haloes in large darkmatter only simulations matches the observed fraction ofmassive quiescent galaxies (~10¹⁰-10¹¹M). This strongly suggests that halo accretion rate is the key parameter determining which massive galaxies at z ~ 1.5-3 become quiescent. Empirical models that connect galaxy and halo evolution, such as halo occupation distribution or abundance matching models, assume a tight link between galaxy properties and the masses of their parent haloes. These models will benefit from adding the specific accretion rate of haloes as a second model parameter.