JWST catalogs 164,000 galaxies

University of California, Riverside researchers said on May 11 that they used NASA’s James Webb Space Telescope data to build what they described as the most detailed map yet of the cosmic web, the large-scale network of filaments, clusters and voids that links galaxies across the universe. The work used the COSMOS-Web survey, which the team said is the largest James Webb survey conducted so far. The researchers said they traced structure across 13.7 billion years of cosmic history, back to when the universe was about one billion years old. The study appears in *The Astrophysical Journal*. ### Where does the 164,000-galaxy figure come from? The paper says the reconstruction used roughly 160,000 galaxies with robust photometric redshifts, while UC Riverside’s May 11 release said the public catalog contains 164,000 galaxies and their cosmic density. That appears to explain why social posts this week focused on the 164,000 figure: it refers to the released catalog tied to the map, not just the subset described in shorthand in the paper abstract. (news.ucr.edu) Hossein Hatamnia, a graduate student at UC Riverside and Carnegie Observatories and the paper’s lead author, said COSMOS-Web was designed “from the start” to provide the wide and deep view needed to see the cosmic web. Bahram Mobasher, a UC Riverside professor and Hatamnia’s adviser, said in the university release that the team also released the pipeline used to build the map, the galaxy catalog and a visualization showing the web evolve across billions of years. (arxiv.org) ### What exactly is COSMOS-Web measuring? COSMOS-Web covers a contiguous patch of sky about the size of three full moons, according to UC Riverside and the Phys.org summary of the university release. The survey uses JWST’s infrared sensitivity to detect faint, distant galaxies that earlier observatories could not see as clearly, including objects obscured by dust. (news.ucr.edu) The cosmic web is not a direct image of dark matter itself. The researchers reconstructed large-scale structure from the distribution of galaxies, which trace denser and emptier regions over time. In the paper, the team said it used a weighted kernel density estimation method to rebuild that structure out to redshift about 7, a period corresponding to very early cosmic history. (news.ucr.edu) ### Why are astronomers paying attention to this release now? May 11 was the date of UC Riverside’s announcement, and social posts spread in the following days as astronomy accounts highlighted the 164,000-galaxy catalog and the cosmic-web maps. The attention centered on the combination of scale and depth: a wide-area JWST survey, a public release, and a map extending close to cosmic dawn. (phys.org) The paper’s title is “Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to z ∼ 7 with the Largest JWST Survey.” The authors wrote that the dataset lets them examine how galaxy properties vary with environment across cosmic time, rather than only in the nearby universe. ### What does the study say about galaxy evolution? The authors reported that stellar mass correlates positively with density at all redshifts they examined. (news.ucr.edu) They also wrote that dense environments appear to be associated with earlier mass assembly, while lower-mass galaxies show stronger suppression of star formation at later times. Those are the study’s findings, not an independent verdict about all galaxy formation models. (iopscience.iop.org) UC Riverside said the new map is more informative than earlier maps of the same sky region made with Hubble data. Mobasher said a side-by-side comparison showed how previous-generation observations had smoothed over structure that JWST now resolves in greater detail. ### Where can researchers go next with the dataset? The next step is not another announcement date but broader use of the released material. (arxiv.org) UC Riverside said the large-scale-structure maps, the processing pipeline, the 164,000-galaxy catalog and an animation of the evolving cosmic web have been released publicly. The paper is already published in *The Astrophysical Journal*, giving outside researchers both the methods and the data products to test related questions about galaxy environments and early structure formation. (publicnow.com)