Contributed Talk - Splinter Computation

Friday, 25 September 2020, 09:54   (virtual room B)

The Elephant in the Bathtub: When the physics of star formation drive the baryon cycle of galaxies

Jindra Gensior, Benjamin Keller, Diederik Kruijssen
ARI/ZAH Universität Heidelberg

Recent observational studies find that the star formation efficiency (SFE) varies both between and within galaxies. In addition, early-type galaxies and galaxy bulges exhibit a star formation rate that is suppressed compared to spiral galaxies despite containing similar amounts of molecular gas, thereby suggesting that star formation is not solely regulated by gas density. However, numerical simulations often use a sub-grid model for star formation with a constant SFE and a gas density dependence only, in contradiction to these observations. I will present a new sub-grid star formation model for the moving-mesh code Arepo which can be used in cosmological simulations and for isolated galaxies. It includes an SFE dependence on the gas dynamics, in accordance with the latest observational and theoretical results. I will discuss this model in the context of star formation quenching, to assess whether the deep gravitational potential of stellar spheroids can induce enough shear to influence the galactic dynamics and thus suppress star formation, and contrasting with the classical sub-grid star formation prescription. I will present a suite of hydrodynamics simulations of isolated galaxies, ranging from disc galaxies to spheroids with gas-to-stellar mass ratios of 1 to 20%. This enables a detailed exploration of how differences in the gravitational potential/morphology change the properties of the gas and the SFE.  I show that the shear generated by the deep gravitational potential of bulges can suppress star formation in the central regions of galaxies by altering the dynamical state of the gas and rendering it supervirial. This dynamical suppression of star formation is enhanced at higher stellar surface densities and lower gas fractions but only captured with the new star formation model. Furthermore, I demonstrate that the resultant ISM structure (gravitational stability, resulting clumpiness, velocity dispersion) is also strongly affected by gas fraction and morphology. Together, these physical mechanisms drive the simulated spheroid-dominated galaxies off the main sequence, into the quenched population of galaxies, demonstrating that the physics of star formation can limit and regulate the baryon cycle at low redshifts and high galaxy masses.