Cake Talk by Tobias Looser
Abstract: I will present the discovery of a stellar Fundamental Metallicity Relation, a smooth relation between stellar mass, star-formation rate and stellar metallicity (analogous to the well-established gas-phase FMR). I will discuss how this points to starvation as the main physical process through which galaxies quench at low-z and that this suggests that the metal-poor gas accreted from the intergalactic/circumgalactic medium – or the lack thereof – is continuously imprinted onto the stars over cosmic times. And I will present evidence that starvation is driven by integrated AGN feedback. While local (massive) galaxies predominantly quench slowly through starvation, this might be very different in the high-redshift Universe. Indeed, I will present the discovery of a rapidly (mini-)quenched galaxy at z=7.3 with JWST. This galaxy exhibits a Lya drop, a Balmer break and complete absence of any emission lines. Its SFH consists of a short and intense burst terminating only 10-40 Myr before the time of observation. Crucially, this galaxy has a stellar mass of only 4–6×10^8 M⊙. This suggests that likely different physical mechanisms were dominantly responsible for quenching this galaxy. This galaxy lies in a pivotal mass range between ‘bursty’ and stable SFHs, and in which feedback from a primordial black hole or star formation might drive powerful outflows leading to (temporary) quiescence. Finally, I will present more observational evidence for strongly stochastic star-formation histories of high-redshift and low-mass galaxies based on inferred SFHs of ~200 galaxies (0.6<z<11) from deep NIRSpec prism spectra.