The DESI project

In May 2021, DESI started a five-year campaign to measure accurate redshifts of 40 million galaxies and quasars over 14 000 square degrees, a third of the sky. To do this, it is using a new multi-fiber spectrograph at the Mayall 4-m telescope at Kitt Peak National Observatory, in Arizona (US), equipped with 5000 robotically actuated fibers. By the end of 2021, DESI had already collected the largest spectroscopic dataset to date.

In early 2023, DESI released to the public a planetarium show, “5000 eyes”, that has already been translated into ten languages and shown in more than a hundred planetariums around the world. IFAE contributed to the documentary in different ways: Andreu Font-Ribera is one of the few scientists interviewed in the documentary; Marc Manera coordinated the Catalan version of the documentary; Santiago Ávila contributed to the Spanish translation. The documentary has already been shown in several planetariums in Catalonia, including four passes in the CosmoCaixa planetarium (the largest one in Catalonia).

Later in June, the first batch of data from DESI was made publicly available in the Early Data Release (EDR). Taken during the experiment’s “survey validation” phase, the data include the spectra of nearly 2 million distant galaxies and quasars as well as stars in our own Milky Way. The release of this data was accompanied by a group of publications presenting some of the early scientific results from DESI and descriptions of the instrument and survey operations. Two of these publications were led by PhD students at IFAE. Cesar Ramírez-Pérez led a first article describing the Lyman alpha forest dataset [1]. The Lyman alpha forest is a set of absorption features in the absorption of very distant quasars that allows us to map the distribution of neutral hydrogen in the Universe. Calum Gordon led a second article presenting the first measurement of 3D correlations in the Lyman alpha forest of DESI [2]. These publications are important milestones towards the measurements of the expansion rate of the Universe with DESI, expected for mid 2024.