Dissecting the mass quenching in TNG50: Galaxy size determines the quenching mode

TL;DR

This study reveals that galaxy size influences the mode of quenching, with small galaxies rapidly quenched by kinetic AGN feedback and larger ones gradually quenched through suppressed gas inflow, based on TNG50 simulation analysis.

Contribution

It demonstrates that galaxy size is a key factor in quenching mechanisms, highlighting the dual role of kinetic AGN feedback in both immediate and long-term quenching processes.

Findings

Small galaxies are quenched rapidly within 1-2 kpc by kinetic AGN feedback.

Large galaxies experience gradual quenching due to suppressed gas inflow over Gyr timescales.

Kinetic AGN feedback affects both central regions and overall gas supply, influencing galaxy evolution.

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.