The existence of filaments connecting galaxies, within which galaxies form, has been a long-standing prediction of structure formation theories in a Universe dominated by cold dark matter. However, direct imaging of these filaments has remained elusive until the advent of large-format integral field spectrographs such as the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope.
In this talk, I will present recent direct detections of cosmic web filaments in Lyα emission from an ultra-deep (142-hour) observation in the MUSE Ultra Deep Field. This unique dataset enables us to directly probe the morphology, surface brightness profiles, and the transition radius between the circumgalactic and the intergalactic medium of different extended emitting structures spanning 3-5 cMpc. These filaments are observed both between a pair of bright quasars at redshift z~3.22 and within overdensities of Lyα emitters at z ~2.8 and ~4. I will also compare these findings with predictions from numerical simulations.
These results mark a significant step toward mapping the large-scale structure of the Universe in emission, offering a direct tracer of dark matter distribution and gas dynamics. Looking ahead, I will discuss how current and future instruments can extend these results. MUSE continues to be crucial for deep Lyα observations, while the upcoming BlueMUSE will expand coverage at lower redshifts. Further ahead, proposed projects such as WST could enable statistical studies of filamentary structures across cosmologically relevant volumes.
Mapping the Cosmic Web in Lyα emission around Quasars and Non-AGN Systems