Galaxies in their cosmic web

Principal Investigator: Gabriella De Lucia


  • Structures in the Universe and Emergent Phenomena


This research line tackles different aspects of galaxy formation and evolution, making use of both observational data taken at major ground and space-based facilities and state-of-the-art theoretical models. Our research focuses on: studying how galaxy properties and their evolution with cosmic time are affected by the galaxy location within the large scale structure (from voids, to filaments, groups, and up to the largest structures of clusters and proto-clusters); analysing the impact of the energetic feedback from massive stars and Active Galactic Nuclei on the stellar population and gas properties of galaxies; studying the dynamics of massive Black Holes and their expected gravitational wave signal; making dedicated forecasts for planned observational experiments, including the recently launched Euclid satellite and the future Square Kilometre Array Observatory.

Status of project and perspectives:

The research carried out by our team focuses on different aspects of galaxy formation and evolution. This field lies at the interfaces of astronomy, particle physics and cosmology, with elements of all these three disciplines needed in order to understand how galaxies form and evolve in a cosmological framework. In turn, galaxies provide the primary tracers adopted by a number of different cosmological probes. Therefore, a better understanding of the galaxy formation process is crucial to improve our knowledge of the mass-energy content of the Universe.

Our team includes strong expertise in the development of state-of-the-art theoretical models of galaxy formation. In particular, the team includes the main developers of the GAlaxy Evolution and Assembly (GAEA) model that enables simulations of galaxy formation in large cosmological volumes and at different cosmic epochs, and the core developers of OpenGADGET3, a TreePM+SPH code including an explicit treatment for hydrodynamics. We use our theoretical tools to address different scientific questions including studies of: i) how galaxy formation and evolution vary in different environments (as characterised by the location of galaxies in their “cosmic web”) and across cosmic time (from galaxies in the Local Group to galaxies in what we believe to be the progenitors of local massive systems, i.e. “proto-clusters”); ii) black hole (BH) dynamics and the co-evolution of supermassive BHs and their host systems for a wide mass range of BHs and galaxy hosts; iii) pristine environments, the origins of molecules and heavy elements in the Universe, as well as the birth of the very first generations of stars and galaxies, (iv) the formation of stellar clusters and their dynamical evolution within galaxy haloes. Our theoretical studies are well renowned by the astronomical community, as demonstrated by the active involvement of team members in a number of medium-to-large observational programmes to aid the interpretation of observational data or even guide the conception and design of future observational programmes and strategies. For example, members of our team have provided dedicated mock catalogues to the Euclid consortium both to make dedicated predictions in the pre-launch phase, and to prepare for the interpretation of the data that the consortium will soon start collecting. We are also actively involved in the SKA working groups to make dedicated forecasts for specific experiments and optimise the future survey strategy (see below). Finally, several members of our teams have been making predictions for the observable gravitational wave signals from massive black hole binaries in the band of the Laser Interferometer Space Antenna (LISA) and in the band of pulsar-timing array (PTA) experiments.

Virtually all theoretical investigations mentioned above are paralleled, in our team, by a strong involvement and leadership role in dedicated observational programmes. In particular: members of our team carry out studies of galaxy formation and early chemical enrichment of the galactic building blocks in the Local Universe through active involvement in the Euclid consortium and the ASKAP collaboration. More specifically, we study how physical properties of local star-forming dwarf galaxies (that are possible analogues to the high-redshift progenitors of today’s larger systems) vary as a function of environment, from the inner to the outer regions of galaxy clusters, out to large voids. Several members of our team are involved in the investigation of high-redshift clusters and protoclusters, with a focus on their galaxy populations, by exploiting multiwavelength observations from the major ground- and space-based facilities. In particular, we investigate the impact of early cluster progenitor environments on galaxy population properties (concerning star formation and nuclear activity, galaxy structure, gas reservoirs), especially across the transition epoch between the proto-cluster and established cluster regimes. By comparing observations and theoretical predictions within a cosmological framework, we aim at constraining the nature of environmental effects tweaking galaxy evolutionary paths already at early times. In this context, we also investigate the observed diversity of galaxy population properties in high-redshift (proto-)clusters, and its relation with (proto-)cluster properties. Our understanding of galaxy populations in these early massive structures is also a critical element in the definition and interpretation, especially at high redshift, of cluster samples identifying clusters based on their galaxies, for both astrophysical and cosmological investigations. Finally, we also use multi-wavelength observations across the spectrum to study the properties of Active Galactic Nuclei and their supermassive BHs and host galaxies across cosmic time, investigating the impact of nuclear activity on galaxy properties from the nearby Universe up to z≳6.

We are also actively involved in different cosmological investigations. In particular, members of our team are part of the Euclid Consortium and are involved in activities related to the cosmological exploitation of galaxy clusters. Members of our team are also actively involved in different Science Working Groups of the SKA Observatory (SKAO). This powerful radio telescope will measure the signal from the 21cm line of neutral hydrogen conducting deep HI observations of millions of galaxies out to z>1, and creating tomographic intensity maps of the HI distribution out to z~6. These new data promise to revolutionise our understanding of the Universe providing measurements of the matter distribution at cosmological scales and of the HI content of galaxies at different cosmic epochs. Members of our team have coordination responsibilities within the SKA Cosmology Science Working Group, and are actively involved in projects aimed to (1) explore the potential of different survey strategies by building dedicated cosmological forecasts, based e.g. on peculiar velocity measurements, or cross-correlations between intensity mapping and different galaxy surveys; (2) analyse first-of-their-kind data coming from precursors’ observations (MeerKAT). These activities will help shape the SKA survey design, putting team members at the forefront for taking leading roles within SKA Key Projects.