Drifting through the Cosmic Web

The Large Scale Structure of the Universe (LSS) was first discussed at the IAU Symposium No. 79 in 1977 in Tallinn. The title of the Symposium : “The Large Scale Structure of the Universe” , was the first official use of this term (J. Einasto). Since then, it has been of major interest in cosmology. This large scale pattern, emerged from the primordial density fluctuations of dark matter under the effect of gravity, is composed of nodes, filaments and walls surrounding large voids: it is a vast foam-like structure, aka the “cosmic web”, which provides constraints on the content of the universe and the nature of its components.

Beyond its cosmological interest, the cosmic web also constitutes the astrophysical context in which galaxies form and evolve. Indeed impressive progress in observations, theory and numerical simulations have provided new insights into its relation to the properties of galaxies. High resolution spectroscopy revealed that over 90% of the baryonic mass resides in tenuous filaments, the intergalactic medium (IGM), which is mostly ionized and follows the LSS pattern. Baryons and energy are exchanged through complex phenomena between this huge gas reservoir flowing through the cosmic web and the galaxies, driving their evolution. Terrific developments in high-performance computing have allowed hydro-dynamical simulations to include both gravitational interactions and astrophysical processes with unprecedented accuracy and thereby to follow the dynamics of the gas over an extremely large dynamic range. Such simulations show that filamentary cold flows of gas can penetrate the central regions of galaxies and trigger efficient star formation activity, a process expected to be more effective or common at high redshift. Cold flows could also contribute to the build up of the galaxies’ angular momentum. These phenomenons illustrate the intimate link between the large scale filamentary flows of the gas and galaxy properties. At the same time, the completion of large scale spectroscopic surveys, such as SDSS and GAMA at low redshift and VIPERS at higher redshift, have dramatically improved the characterization of the LSS. Multi-wavelength photometric surveys and radio surveys (yielding SFR, mass, gas content, metallicity, etc.), high-resolution imaging (morphologies) and IFU spectroscopy (infall, outflows and galaxy-IGM interplay), are allowing us to study the evolution of the anisotropic IGM and the properties of galaxies simultaneously, using the cosmic web as the natural “metric” of galactic evolution. The overwhelming amount of data expected from the future generations of spectroscopic surveys (eBOSS, PFS-SuMIRe, DESI, Euclid) and radio surveys (LOFAR, ASKAP, SKA, etc.) will push further this investigation of the influence of environment in shaping galaxy properties. This exciting observational, numerical, and theoretical effort is making it possible at last to bridge the investigation of cosmic structures from cosmological scales all the way down to galactic scales. It is therefore timely to gather theorists, simulators and observers to brainstorm over a topic that has emerged at the forefront of extragalactic astronomy and cosmology: The relationship between the physical and dynamical properties of galaxies and the structure and evolution of the cosmic web. It is the goal of this conference to review the achievements and challenges in this field.

In particular, the following questions will be discussed during the meeting:

  • What is our theoretical understanding of the LSS, its dymanics and its effects on small-scales? (3D structure of the dark matter field, mechanism of acquisition of angular momentum of collapsed structures, dynamics of gas accretion)
  • What is the status of numerical simulations? Which techniques should be implemented to optimally move from coarse-grain to fine-grain modeling? What are the numerical and analytical challenges of zooming techniques?
  • Which algorithms can be used to extract the components of the cosmic web, i.e. nodes, filaments, walls and voids? How efficient are they? What are the observational difficulties in applying them to actual galaxy and HI surveys?
  • Gas web vs galaxies web: Where is the gas in the 3D structure traced by galaxies? What do we know about the relationship between the LyA forest and the cosmic web? How do galaxies accrete and reject gas from and into the cosmic web?
  • What are the observational signatures of the connections between galaxy properties and their location within the cosmic web? (the role of environment in star-formation, star-formation quenching, feedback, inflows, outflows, angular momentum acquisition and metal enrichment)
  • How will future spectroscopic and HI surveys improve the current picture?
  • Can observations discriminate between GR and alternative theories of gravity ?