Speaker: Jindra Gensior (MPIA)
Title: The Elephant in the Bathtub: When the physics of star formation regulate
the baryon cycle of galaxies
Abstract:
Recent observational studies point towards a decreasing gas fraction and a low star formation efficiency (SFE) as the key drivers for star formation quenching in galaxies. However, what drives this SFE decrease, especially in early-type galaxies, is unclear. One proposed mechanism, morphological quenching, suggests that the global galactic environment can affect the gas dynamics such that star formation is heavily suppressed. I will present a suite of hydrodynamic simulations of isolated galaxies, which includes a new sub-grid star formation model capturing the influence of galactic dynamics on the SFE via the virial parameter of the gas. The parameter space spanned by the simulations ranges from disc galaxies to spheroids, with initial gas fractions between 1 and 20%. This enables a detailed exploration of how differences in the gravitational potential/morphology change the properties of the gas and the SFE, as well as how it interlinks with the gas fraction. 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. 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.