RadioGaGa — Enabling Radio intensity mapping: cosmic Gas and its link to Galaxies
What's behind the Universe's most abundant components: dark matter and dark energy? How do the processes shaping galaxies truly work? Hydrogen Intensity Mapping experiments (HI IM) are opening new frontiers in our quest to answer those questions, producing detailed three-dimensional maps of a significant fraction of the Universe and probing the distribution and cosmic abundance of neutral hydrogen (HI), the principal fuel of stars.
While HI IM promises to revolutionise our understanding of the Universe, capturing its elusive signal is no easy feat. One major challenge is separating the true (and faint) cosmic signal that the extragalactic hydrogen emits in the radio band from overwhelming contaminants (an intricate mixture of instrumental spurious signals and intense galactic emissions), a problem the RadioGaGa project tackled head-on by crafting cutting-edge statistical learning techniques tailored for HI IM data.
RadioGaGa was a 2-year research project (run through 2023 and 2024) supported by the European Union's "NextGenerationEU" programme and carried out at the Astronomical Observatory of Trieste, part of INAF. Its goal has been to pave the way for HI IM experiments in astrophysics and cosmology, unlocking the potential of advanced radio arrays like the upcoming SKA Observatory.
Results' highlights:
- The HI IM signal was measured in cross-correlation with a galaxy survey, achieving unprecedented accuracy (Carucci et al., 2025). Compared to older standard practices, we could bypass the need to reconstruct the lost signal due to contaminants' separation. This allowed the quantification of the cosmic amount and spatial distribution of HI, while successfully testing the signal-processing tools from RadioGaGa.
- Processed observations from the MeerKAT radiotelescope used in the measurement above are publicly available on the MeerKLASS collaboration website.
- Building on the breakthrough described above, we analysed newer MeerKAT HI IM data and achieved the world's first direct and independent detection of the HI IM signal at cosmological scales (MK collaboration, 2026, submitted). This achievement highlights the potential of HI intensity mapping for future cosmic surveys with the SKA Observatory, for which MeerKAT serves as a precursor.
This project was supported by the "NextGenerationEU" programme, in the context of the "Piano Nazionale di Ripresa e Resilienza (PNRR)" [PNRR-4-2-1.2]