The multi-scale cosmic web is the environment in which galaxies form and evolve. Gas flows along walls and filaments, penetrates within dark matter haloes and brings to the galaxies both angular momentum and fuel for star formation. Recent observational studies at low and intermediate redshifts have shown evidence that the cosmic web environment (e.g. proximity to cosmic filaments, or number of filaments connected to the galaxies sitting at the “nodes”) modulates galaxy mass assembly beyond the mere effect of halo mass and local density. I will briefly review these works and present in more details the analyses that we carried out on the photometric field COSMOS as a pilot study for EUCLID, with the help of well-calibrated mocks. Based on results from hydrodynamical simulations, I will explain why we indeed expect that the multi-scale cosmic web plays an important role in shaping the diversity of accretion histories onto galaxies at fixed mass and density, and I will highlight the difficulties that we have to face observationnally to confirm this scenario.
In particular, the connection between galaxies and the cosmic web should be stronger at high redshift (z>2), when the environment is gas-rich and coherent gas streams are not yet strongly altered by e.g. gas shock heating and feedback. At these redshifts though, large and complete surveys with accurate enough galaxy redshift measurements are extremely costly, which makes the cosmic web reconstruction on large volumes being a real challenge. Based on realistic forecasts from hydrodynamical simulations I will discuss how future lyman-alpha surveys carried out with upcoming facilities (e.g. WEAVE, PFS, MOSAIC) can be a game-changer to understand and quantify the co-evolution of galaxies and the cosmic web at high redshift.
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