High dust contents in high-z quiescent galaxies: how dusty galaxies evolve in the SIMBA simulation

Recent observations with instruments such as JWST and ALMA are increasing the number of high redshift measurements of interstellar medium (ISM) in quenched (or quiescent) galaxies (QGs), that is galaxies with little to no trace of star formation. This is providing a way to connect the process of quenching of the star formation with the feedback mechanisms evolving the ISM. Large statistical samples are, however, still difficult to obtain due to the faint nature of the ISM in QGs. In this framework, cosmological hydrodynamic simulations provide means to study the properties of a large number of objects, furthermore testing the physics of feedbacks and their influence on the evolution of the ISM component directly. This will pave the way for future targeted observations, by providing physically motivated tools for the prediction of ISM content in QGs. We use the state-of-the-art SIMBA cosmological simulation to trace the evolution of dust and cold gas in the ISM for QGs up to redshift z~2. We find that in SIMBA the fraction of QGs with large amounts of dust is particularly significant at high redshift (z>1.5-2). SIMBA furthermore predicts that the observed bimodality in the distribution of quenching timescales is not affected by the environment and does not strongly correlate with the age or mass of the galaxy. Moreover the effect of the environment, including mergers, only partially explains the presence of dusty-QGs, and internal mechanisms such as the energy input from an active galactic nucleus (AGN) are generally far more effective in the removal of dust in the ISM, whether is over fast or slow quenching modes. The effectiveness of the mechanisms is rather independent of the presence of cold gas, and of the timescale of its removal, setting clues for separate pathways of gas and dust evolution. The division is likely generated by a mechanism of dust re-growth in the ISM, adding complexity to the intricate scenario of galaxy quenching by cold dust and gas feedback.