The discovery of dusty star-forming galaxies (DSFGs) as major contributors to the Cosmic Infrared Background has transformed our understanding of galaxy evolution. With star formation rates reaching hundreds to thousands of solar masses per year, these galaxies account for a substantial fraction of cosmic star formation, yet the molecular gas reservoirs that fuel their activity and the physical conditions of their interstellar medium (ISM) remain challenging to constrain. In this talk, I will present results from VLA Vz-GAL, a large survey of CO(1-0) emission in 106 DSFGs at redshifts 1 to 6, exploring what these observations reveal about their molecular gas reservoirs. I will then introduce TUNER, a state-of-the-art turbulent, non-LTE radiative transfer framework that jointly models dust continuum and molecular-line emission to infer the physical conditions of the ISM. Finally, I will discuss how extending this approach to incorporate ISM heating and chemistry can help connect the molecular gas physics of high-redshift DSFGs and quasar hosts with that of local ultraluminous infrared galaxies, offering a broader perspective on the processes that regulate galaxy growth across cosmic time

The interplay between the interstellar medium (ISM), star formation, and stellar feedback is a key driver of galaxy evolution across cosmic time. Exactly how this happens, and whether this cycle changes depending on the galactic environment, is still highly debated. Nearby galaxies (<10Mpc) offer the perfect laboratory, where current facilities such as ALMA, JWST and HST reach cloud-scale (<100pc) resolution, thus serving as a bridge between detailed studies in our own Galaxy and integrated measurements from more distant objects.

I will first present our work on studying the resolved properties of the ISM using an innovative extinction imaging technique, which exploits space-based optical data to map the dust (and gas) content of nearby disc galaxies at 0.1” resolution (~5pc). Our study of M51 using this technique has shown that there are clear changes in the properties of the ISM depending on the galactic environment, as well as on the type of spiral potential felt by the gas, which were missed by previous cloud studies of this galaxy.

On the other hand, stellar feedback has been highlighted to be a major contributor to the observed inefficiency of star formation at cloud-scales. JWST now allows us to unveil the still emerging young star clusters (YSCs) within the dusty clouds, which are still actively driving stellar feedback. I will showcase our pilot NIRSpec/MOS survey of emerging YSCs in NGC628, as part of the Feedback in Emerging extrAgalactic Star clusTers (FEAST) project. Spectroscopy in the 1-5 micron range highlights the chemical complexity of these star-forming regions, simultaneously probing the HII regions and photodissocation regions (PDRs). As YSCs age, they become less embedded, with a fainter, less compact PDR. I will show how the radiation field is affecting the polycyclic aromatic hydrocarbon emission associated with these emerging YSCs.