Speaker
Description
Directly observing the first quenched galaxies and understanding the feedback mechanisms that shaped their star-formation histories (SFHs), quenching and baryon cycles is crucial for constraining galaxy formation models. Prior to JWST, quenched galaxies were only identified up to z < 4, and high-redshift (z > 3) quenched galaxies were exclusively massive (M⋆ > 10^10 M⊙). JWST has now pushed this frontier to z ~ 7–8, uncovering a surprising diversity: not all quenched systems at these epochs are massive.
The SFHs of so-called "mini-quenched" galaxies suggest rapid and recent quenching on timescales of tens of Myr. Their quenching is likely driven by internal feedback mechanisms, such as outflows triggered by intense star formation or accreting black holes, which expel the ISM and halt star formation. Afterwards, renewed gas inflows may lead to rejuvenation, consistent with bursty SFHs through stochastic baryon cycles, as predicted by simulations of early galaxies. Additional evidence for bursty SFHs comes from scatter around the MS and variations in star formation rates across different timescales.
To test this theoretical framework and establish the feedback mechanisms which drive bursty star formation, I will present the first results from a novel deep 74-hour JWST-NIRSpec survey designed to investigate bursty star formation through SFH and ISM studies. Our program targets a diverse sample of high-z galaxies in all stages of star formation, crucially including faint and previously under-represented mini-quenched and "lulling" galaxies (i.e., those with low specific star formation rates below the MS).
I will highlight how mini-quenched and lulling galaxies offer unique insights, as their stellar populations and ISM are imprinted with their past assembly histories. In particular, I will present the first study of the ISM conditions in lulling galaxies, using a sample of ten such systems at z > 5, for which I will examine the ionization state and metallicity of the residual gas and explore whether the ionization is driven by residual star formation, AGNs, or shocks.
Finally, I will show how our program quantitatively constrains bursty SFHs, illuminates the transition from temporary quenching and episodic star formation to permanent quenching and secular evolution, and paves the way for future JWST studies on feedback-regulated star formation at high redshifts.
