Affiliation: University of Cambridge

Contribution: Oral

Title: Discovery of a recently (mini-)quenched galaxy at z=7.3 and more observational evidence for bursty SFHs in the first billion years

Abstract: Directly observing the first quenched galaxies – i.e. galaxies with no or negligible star formation activity at the epoch of observation – and determining the causes which quenched them (perhaps only temporarily), is of utmost importance to constrain models of galaxy formation and transformation. Before JWST, quenched galaxies have been identified out to z<5; and are all found to be massive (M⋆ > 10^10 M⊙). I will present the discovery of a recently (mini-)quenched, post-starburst galaxy at z=7.3. 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 is a significantly lower stellar mass than any known high-redshift quenched galaxy (redshifts 3<z<5), yet it is much larger than the maximum mass of reionization-quenched dwarf galaxies in simulations. The fact that the galaxy does not have any close companions rules out environmental quenching. 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. In addition to this discovery, I will present more observational evidence for an extremely stochastic evolution of high-redshift and low-mass galaxies based on inferred SFHs of ~200 galaxies (0.6<z<11) from deep NIRSpec prism spectra.

This contribution can be found here (pdf).