🔭 Lyman-alpha Nebulae Everywhere in the Young Universe
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These structures, named Lyman-alpha nebulae, appear around galaxies when the Universe was only 2 to 4 billion years old, during a phase of intense activity called the Cosmic Noon. It was at this time that star formation reached its peak, a process requiring enormous quantities of hydrogen, the fundamental building block of stars.
An enormous hydrogen gas halo detected in HETDEX data and overlaid on its location as seen by the James Webb Space Telescope (JWST). Present 11.3 billion years ago, this system shines with the combined light of many galaxies, with the brightest region in red. Thanks to HETDEX, the number of known halos has increased more than tenfold.
Credit: Erin Mentuch Cooper (HETDEX), JWST image: NASA, ESA, CSA, STScI.
This observation is the result of the HETDEX project, which is mapping over a million galaxies to analyze dark energy. Using the Hobby-Eberly Telescope, one of the world's largest instruments, astronomers have captured the faint signals emitted by ionized hydrogen near galaxies. Their work has uncovered the presence of tens of thousands of these halos, creating a statistical catalog of unprecedented scale for the scientific community.
The studied halos display an impressive range of shapes and sizes. Some resemble oval clouds enveloping a solitary galaxy, while others adopt irregular contours and encompass several galaxies.
To identify these halos, researchers targeted the brightest galaxies identified by HETDEX. Nearly half of them showed the signature of a surrounding halo. However, this proportion could be larger, as the dimmer systems remain difficult to observe completely.
The significant expansion of this catalog offers new avenues for exploring the early Universe. Scientists can now dedicate themselves to an in-depth analysis of the halos, allowing them to test and refine models describing galaxy formation. This approach will help clarify how matter is distributed and evolves in the cosmos.