China's FAST Radio Telescope Maps Record Neutral Hydrogen Galaxy Catalog

Researchers utilizing China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) have released the second data batch of the FAST All Sky HI survey (FASHI DR2), establishing the world's largest catalog of neutral hydrogen galaxies. Led by Jiang Peng's team at the National Astronomical Observatories of the Chinese Academy of Sciences, the survey captured 156,000 neutral hydrogen galaxies covering nearly half the celestial sphere. The dataset expands previous international sky survey records fivefold and sharpens measurement precision of nearby cosmic neutral hydrogen density to 0.6 percent, providing critical observational baselines for galaxy evolution and dark matter studies.

Neutral hydrogen serves as the foundational building block of galaxies, emitting a 21-centimeter radio signal capable of piercing interstellar dust to reveal deep cosmic structures. By raising the measurement precision of neutral hydrogen density in the local universe to 0.6 percent—the most precise reading recorded to date—the survey delivers a massive empirical baseline for global astrophysicists examining large-scale cosmic structure, gravitational-wave origins, and dark matter distribution.

A research team led by Jiang Peng at the National Astronomical Observatories of the Chinese Academy of Sciences has published the second dataset from the FAST All Sky HI survey, known as FASHI DR2. According to state media reports, the release establishes the world's largest catalog of neutral hydrogen galaxies, covering roughly half the celestial sphere. The newly released dataset catalogs 156,000 neutral hydrogen galaxies, a figure that is five times larger than those produced by prior international radio surveys and nearly four times the scale of FAST's initial survey data. Neutral hydrogen, regarded by astrophysicists as the primordial building block of cosmic structures, emits faint radiation at a wavelength of 21 centimeters. These signals can penetrate thick layers of interstellar dust, allowing instruments to probe the far reaches of the universe without optical obscuration. Leveraging the expanded catalog, the team refined the measurement precision of neutral hydrogen density in the nearby universe to 0.6 percent. Chinese astronomical authorities described this as the most precise measurement of this physical quantity achieved to date. The dataset was produced through collaboration among several domestic scientific institutions and is intended to support investigations into galaxy formation, the distribution of dark matter, and large-scale cosmic structure. Beyond basic cosmological modeling, researchers noted that the high-density catalog will serve as an essential observational reference for tracking gravitational-wave sources and designing future radio astronomy facilities. State reporting indicated that the findings were submitted to and published in an academic journal on September 8, marking a significant operational milestone for the Five-hundred-meter Aperture Spherical radio Telescope located in Guizhou Province.