Unravelling the Cosmic Web with fluorescent emission

2026-07-22

Our cosmological model predicts that most of the matter in the universe is distributed in a network of filaments - the Cosmic Web - in which galaxies form and evolve. Because most of this material is too diffuse to form stars, its direct imaging has remained elusive for several decades leaving fundamental questions still open, including: what are the morphological and kinematical properties of the Cosmic Web on both small (kpc) and large (Mpc) scales? How do galaxies get their gas from the Cosmic Web? In this programme, I will tackle these questions with an innovative method and technology that allows us to directly detect in emission the gaseous Cosmic Web before the peak of galaxy formation, when the universe is less than 3 billion years old: using bright quasars and galaxies as “cosmic flashlights” to make the gas “fluorescently” glow. Although challenging, detecting such emission is possible: I have recently demonstrated that some parts of the Cosmic Web illuminated by bright quasars can be detected in both hydrogen Lyman-alpha and H-alpha emission. These pilot studies and new instruments such as VLT/MUSE and the James Webb Space Telescope (JWST; available from 2021) are the ideal stepping stones for a revolution in the field, the main goals of this programme: 1) direct imaging of the average Cosmic Web extending on cosmological scales (tens of Mpc) in the young universe, away from quasars; 2) revealing the small-scale distribution (below one kpc) of gas within Cosmic Web filaments. For this aim, I will use the deepest available observations to date, including a 160-hours deep integration that is being obtained through our MUSE Guaranteed Time of Observations, and future ground-based Adaptive-Optics and JWST infrared H-alpha observations. These datasets will be combined with new data analysis methods and numerical models that will be specifically developed in this programme opening up a completely new window to study cosmic structure and galaxy formation.

Italy

2026-02-01