The complex relationship between black hole feedback, star formation, and stellar bars in <scp>TNG50</scp>

ABSTRACT We use the cosmological magneto-hydrodynamical simulation TNG50 to study the relationship between black hole feedback, the presence of stellar bars, and star formation quenching in Milky Way-mass disc galaxies. Of our sample of 198 discs, 125 develop stellar bars that last until $z=0$. Tracking their evolution from $z=4$ to 0, we demonstrate that barred galaxies tend to form within dark matter haloes that become centrally disc dominated early on (and are thus unstable to bar formation) and typically host central black holes that grow more rapidly than those of unbarred galaxies. As a result, most barred galaxies eventually experience kinetic wind feedback that operates when the mass of the central supermassive black hole exceeds ${M_{\rm {BH}}} \gtrsim 10^8\, {\rm {\rm M}_{\odot }}$. This feedback ejects gas from the central disc and rapidly quenches barred galaxies of their central star formation, resulting in persistent 3–15 kpc wide holes in the centres of their gas discs; bar formation itself does not significantly affect the central star formation in this model. Interestingly, bars almost always form before gas holes, but if kinetic black hole feedback occurs in a previously unbarred galaxy, bars rarely form thereafter. Consequently, most barred galaxies develop gas holes from ejective black hole feedback, though a gas hole alone does not guarantee the presence of a stellar bar. This subtle relationship between black hole feedback, cold gas disc morphology, and stellar bars may provide constraints on subgrid physics models for supermassive black hole feedback.