Dissecting the mass quenching in TNG50: Galaxy size determines the quenching mode
Haochen Jiang, Enci Wang, Kai Wang, Chengyu Ma, Xu Kong
TL;DR
The study investigates how galaxy size modulates mass quenching in massive central galaxies. It analyzes 46 massive quiescent centrals from the TNG50 simulation, focusing on the timing of kinetic AGN feedback and its dependence on size. Kinetic feedback triggers a two-stage quenching: a short-term, intense suppression within the central $1-2$ kpc and a long-term reduction of gas inflow that can quench the entire galaxy, with compact systems quenching rapidly and larger systems quenching more gradually via strangulation. This size-dependent, two-phase mechanism provides insight into the observed size–quenching relation and offers guidance for implementing AGN feedback in cosmological simulations.
Abstract
The diminishing of star formation is accompanied by size differentiating, as quiescent galaxies are more compact than star-forming galaxies at fixed stellar mass. In order to understand how galaxy quenching is related to galaxy sizes, we performed a demographic study of 46 massive quiescent central galaxies with stellar mass from $10^{10.5}\rm M_\odot$ to $10^{11}\rm M_\odot$ in the TNG50 simulation. We found that, in addition to the triggering active galactic nucleus (AGN) feedback, galaxy size is also a major determinant of the quenching process, as small and compact galaxies are immediately quenched by the kinetic AGN feedback, while galaxies with large sizes are still active until strangulated by the cutoff of new gas replenishment. Further spatially resolved inspection reveals that this short and intense kinetic AGN feedback can only suppress the star formation within 1-2 kpc, resulting in this size-dependent effect of quenching. We also identify a long-term effect of a few Gyr timescale that the gas inflow rate is progressively suppressed after triggering kinetic feedback, which appears to effectively quench large galaxies entirely. We conclude that kinetic AGN feedback has two key roles in quenching: a short-term, intense effect that quenches the central 2 kpc region, and a long-term effect that suppresses the gas inflow rate and further quenches the entire galaxy.