Reconstructing the histories of remarkable dust-rich quiescent galaxies at z > 2

Significant amounts of dust and cold gas have been recently confirmed in quiescent galaxies (QGs) at the Cosmic Dawn and beyond, challenging the conventional view that these objects have poor interstellar medium (ISM) relative to their stellar mass. Although quantifying the changes in ISM after quenching star formation is a key aspect of late galaxy evolution, the presence of ISM-rich quiescent galaxies raises important questions, e.g., what physical mechanism helps quenched sources sustain or replenish their dust content after star formation ceases?

In this walk, I will present the results condensed from three studies that tackle this question both from an observational and theoretical point of view. The studies unveiled significant fraction of dust-rich quiescent galaxies identified in deep JWST fields up to z~3. By modeling their star formation histories, we find that dust-rich quiescent galaxies result from diverse formation redshifts and transition through different quenching pathways, both slow and fast, and exhibit evolving and complex ISM conditions. I will explain how state-of-the-art models and cosmological simulations help reconstruct the evolutionary history of dust and gas in the observed galaxies. Contrary to some claims, the quenching modes attributed to the AGN feedback are not impacting the dust and cold gas within the same timescales.

I will further elaborate on the main channels for the replenishment of dust in QGs that are identified by linking the observed data with simulations. The key channel for dust re-growth is effective within the first 200 million years following the quenching event, and is much weaker connected to the evolution of a cold gas than previously thought. I will illustrate the impact of this process through the age-attenuation plane of JWST detected galaxies. Finally, I will briefly outline important implications for understanding the nature of dusty quiescent galaxies identified in the first 3 Gyr of the universe's history, in particular, how the presence of ISM dust in quiescent galaxies can severally affect the interpretation of results obtained with ALMA and JWST, as well as selection techniques based on JWST rest-frame colors.