Cosmo – prova - ASTROFISICA ALLA STATALE

The last three decades of cosmological observations and discoveries have led to the establishment of a concordance cosmological model. We have found that the Universe expansion is accelerating, which points to the presence of a positive value of the cosmological constant in Einstein’s equations. We also discovered that most of the matter in the Universe is not made of the particles we know on Earth, but of some sort of ‘dark matter’, yet to be identified. In this scenario, the galaxies and the large-scale structures they inhabit today (see figure) are thought to be the result of the gravitational growth of some initial perturbations of quantum mechanical origin.

Figure 1. The large-scale distribution of about 60.000 galaxies, in a “slice of the Universe” mapped by the VIPERS survey. VIPERS was built by an international team coordinated by our group using the ESO Very Large Telescope to measure galaxy distances. In this figure, each dot corresponds to a galaxy, with size proportional to its B-band luminosity and colour reflecting the intrinsic U-B colour of the object

Our group at UniMI originates from the Advanced Grant of the European Research Council (ERC) awarded in 2012 to support the Darklight project (P.I. L. Guzzo). The goal is to combine front-ranked observations (in particular from galaxy redshift surveys, see Figure 1), simulations and theoretical tools to answer fundamental questions such as:

> What is the origin of the accelerated expansion of the Universe? Is it a simple cosmological constant or a more complicated form of Dark Energy?

> What is the particle nature of dark matter? How strong can it interact with the visible sector?

> How can we test the nature of the initial condition of our Universe? Was there an inflationary phase which seeded the structure we see today?

> Can we use the observation of the largest scales in nature to measure the mass of fundamental particles such as neutrinos?

The answers to these questions are enshrined in the large-scale structure of the Universe, which we measure statistically by reconstructing the 3D distribution of galaxies. We are involved in the two major endeavours to do this, DESI and Euclid. Specifically, our group is a founding member of the Euclid project, with primary responsibility in the overall scientific coordination, as well as in specific working groups and work packages.