Letizia Buglani

Monday, December 9th, 2024
3:00pm - 4:00pm
Marlar lounge, in person & via zoom
Talk: Letizia Buglani, 3:00pm - 3:30pm
Star-formation quenching in massive galaxies at Cosmic Noon: new perspectives from JWST
The study of massive, quiescent galaxies at high redshift is crucial for understanding many physical processes driving galaxy evolution. Recent observations by JWST of such galaxies already in place at z ∼ 4 has opened up questions on how such massive galaxies can form so early in the Universe and what mechanisms hide behind the quenching of their star formation.
We analyze ionized gas emission lines in deep rest-frame optical spectra of 14 quiescent galaxies at 1.7 < z < 3.5 observed by JWST NIRSpec in the COSMOS field, in order to derive information about the underlying sources of ionization and investigate the quenching mechanism. Emission lines are detected with SNR > 3 in 71% of the spectra, indicating the presence of continued ionizing sources in this passive population, while, based on the H-alpha flux, the majority of the sample is indeed found to be quiescent. The quiescent sample is clearly separate from the star-forming population in line diagnostic diagrams, and occupies a region usually populated by active galactic nuclei (AGN). Analysis of the observed line ratios, equivalent widths, and velocity dispersions leads us to conclude that in most cases the gas is ionized by AGN activity, despite the lack of X-ray detections. We estimate generally low value of bolometric luminosity and of Eddington ratios for the central engines, typical of low-luminosity AGN. A subset of the sample also hosts ionized and neutral outflows, with ionized outflows velocities of the order of 1000 km/s.
The general picture emerging from this study is that low luminosity AGN are extremely common among quiescent galaxies at high redshift. Furthermore, we find indications that these low luminosity AGN may play a key role in quenching star formation and in maintaining massive galaxies quiescent from Cosmic Noon up to z ∼ 0.