Unraveling the knots of gaseous Cosmic Web filaments at z 3 through H-alpha emission observations

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 very diffuse, its direct imaging has for long remained elusive, leaving many questions still open, e.g.: 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? Here, we tackle these questions with an innovative method to detect in emission the gaseous Cosmic Web using bright quasars as "cosmic flashlights". In particular, we propose to observe in H-alpha emission two fields at z~3 which contain the largest Cosmic Web filaments - over 4 cMpc in length - discovered so far in deep MUSE Ly-alpha emission searches around bright quasars. Because Ly-alpha is affected by radiative transfer which change both its spatial and spectral distribution, non-resonant H-alpha observations are fundamental in order to directly constrain both the filament densities and kinematics. The filament projected angular sizes are perfectly suited for NIRSpec-MOS which can trace the filaments over their full length capturing, at the same time, several embedded galaxies. Our H-alpha observations will probe structures within the filaments on scales smaller than a few physical kpc directly constraining both their density and kinematics. By relating these quantities to the kinematics and distance from associated galaxies, our result will be fundamental to informing a new generation of theoretical and numerical models in order to reveal the physics of intergalactic gas accretion and galactic outflows

Resolving a Massive Node of the Cosmic Web at z=3

How do galaxies get their gas? What is the morphology and kinematics of the accreting gas and how does this affect galaxy evolution? A recent MUSE observation targeting a quasar at z=3 has finally provided the way to directly address these questions through one of the first images of contiguous Cosmic Web filaments on scales of several comoving Mpc. The filaments converge into a node associated with a large concentration of galaxies: two of these - separated only by 2" - have AGN-like spectra making them one of the few known close-binary AGN at high-z and the only triplet, including the quasar, which is 10" away. Because of the seeing-limited nature of the MUSE observations, the majority of the galaxies associated to the filaments and the AGN hosts are unresolved. To overcome this limitation we propose ACS imaging in two filters sampling the galaxy rest-frame UV continuum emission in order to: i) reveal the relation between the gaseous filaments properties (such as gas densities and kinematics) and the morphological properties (such as size, clumpiness and structural parameters) of the associated galaxy star forming regions in order to study how galaxies form their stars, ii) detect the diffuse UV light associated with galaxy interactions and intergalactic star formation in order to constrain the role of environment in the formation of the stellar and AGN components of the progenitor of today's massive galaxies. The proposed ACS imaging will be the perfect complement to the multi-wavelength, ongoing deep observations with JWST, ALMA and Chandra on this field providing a new window on the study of early galaxy and structure formation in a massive node of the Cosmic Web