Galaxy evolution: a gas perspective
Hebrew University of Jerusalem
Galaxy history is marked by a peak of star formation ten billion years ago and a subsequent drop of the star formation rate (SFR) by an order of magnitude. To understand this evolution, it is crucial to probe the gas reservoirs from which stars are formed. With programs observing the molecular gas phase in typical star-forming galaxies at different epochs, I will present how the cosmic evolution of the SFR is mainly driven by that of the molecular gas fraction. The depletion time associated to star formation indeed only weakly changes with redshift, both at galactic and at sub-galactic scales. I will show that the molecular gas content during the winding-down of star formation does not seem to correlate with morphology, suggesting an ongoing supply of molecular gas to compensate for star formation while bulges grow. In contrast, molecular gas reservoirs can be dramatically depleted in extreme environments such as cluster centres. While structure formation is primarily driven by dark matter (DM) dynamics in ΛCDM cosmology, gas processes can in turn affect the DM distribution at galactic scales. Using theoretical modelling and simulations, I will discuss how outflow episodes and gas density fluctuations induced by stellar feedback can expand both the DM and the stellar distributions and hence provide a simple understanding of the formation of DM halo cores and ultra-diffuse galaxies.