The onset of stellar bars at Cosmic Noon. Bar-driven quenching and AGN co-evolution in a mature disc galaxy

Abstract

Observations with the JWST revealed an unexpected abundance of barred galaxies at Cosmic Noon. However, the physical properties of these early bars are almost unconstrained, as it is their impact in the structural evolution of high-z disc galaxies. In this work, we derived the stellar populations of EGS-24154, a barred spiral galaxy at $z=1.17$. First, we investigated the role of the stellar bar in the early assembly history and structural evolution of the galaxy. Second, we studied the properties of the interstellar medium to shed light on the interplay with the central supermassive black hole. We analysed medium-resolution NIRSpec/IFS data of EGS-24154 through full-spectral fitting and derived light and mass-weighted ages and metallicities. We then reconstructed the spatially-resolved SFH, derived the ionizing mechanisms of the interstellar medium analysing several emission lines, characterized the dynamics of EGS-24154, and constrained the properties of a biconical outflow launched by the AGN. EGS-24154 is a baryon-dominated, gas-rich disc galaxy, which grew more than 90% of its stellar mass when the Universe was ~2 Gyr old. We found that the stellar population of the bar started to form at $z\sim5$, compatibly to the time when the stellar disc started to assemble. We observed a star formation desert in the bar region, which is responsible for quenching star formation over several Gyr. We then interpreted that the feedback from the AGN prevented the growth of central mass concentration, allowing the stellar bar to grow in size and strength. In this first study of spatially-resolved stellar populations of a barred disc galaxy at $z>1$, we demonstrated how stellar bars are key drivers of the early structural and dynamical evolution of disc galaxies. In particular, our results call for a revision of most models of disc and bar formation in early baryon-dominated, gas-rich disc galaxies.