Researchers find neutral hydrogen remains despite falling star formation
Researchers combined observations from China's FAST radio telescope and Arizona's DESI survey to stack neutral hydrogen (HI) signals from about 2.5 million galaxies across nearly one-third of the sky, tracking changes over the past 4.5 billion years. They found star formation was about 2.5 times higher 4.5 billion years ago while HI density was only about 1.4 times higher, showing a much smaller decline in HI than in star formation. The result suggests the decline in cosmic star formation is not simply gas exhaustion but likely involves reduced efficiency converting HI into molecular gas and changes in gas inflow and density.
Neutral atomic hydrogen density changed little despite large star formation decline
Context
Scientists combined FAST and DESI observations and stacked signals from many galaxies. They compared gas and star formation over 4.5 billion years. Next, researchers will study how gas moves and turns into molecular hydrogen.
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