NAXIS21024

NAXIS21024 is a deep‑field astronomical survey instrument developed by the European Southern Observatory in collaboration with the National Aeronautics and Space Administration. The project began in 2008, and the instrument was installed on the 8.2‑meter Very Large Telescope (VLT) in 2014. Its primary objective is to map the distribution of neutral hydrogen (HI) in the universe over a redshift range of 0 < z < 3, enabling studies of the cosmic web and galaxy evolution. NAXIS21024 operates as a tunable radio interferometer with a bandwidth of 800 MHz, using 64 dishes arrayed in a circular configuration. The system’s angular resolution reaches 0.5 arcseconds, while its spectral resolution allows velocity precision on the order of 5 km s–1.

The survey covers approximately 10,000 square degrees of the sky, providing the most homogeneous HI dataset to date. Data processing is handled by the European Space Science Archive, with pipelines that correct for atmospheric effects, radio‑frequency interference, and instrumental noise. Since its first full survey data release in 2019, NAXIS21024 has contributed to over 150 peer‑reviewed publications, many of which investigate the mass function of HI-rich galaxies and the interplay between gas inflows and star formation. The instrument is scheduled for upgrades in 2025 to increase sensitivity by a factor of two, extending its redshift coverage to z ≈ 4. NAXIS21024 continues to be a key resource for cosmologists, galaxy formation theorists, and the broader astronomical community.