JWST maps 164,000 galaxies

The COSMOS-Web project has turned James Webb Space Telescope observations into a public map of 164,000 galaxies, giving astronomers their most detailed view yet of the universe’s large-scale “cosmic web.” The release, highlighted on May 22 by Heise and described earlier this month by the University of California, Riverside and Rochester Institute of Technology, uses JWST data to reconstruct how galaxies trace filaments, clusters and voids across 13.7 billion years of cosmic history. The result matters because the cosmic web is not a picture of individual galaxies alone. It is the larger structure they inhabit: dense filaments and nodes separated by vast, relatively empty voids. Researchers say the new reconstruction reaches back to a time when the universe was less than 1 billion years old, extending direct study of environment-driven galaxy evolution much deeper into the early universe than earlier surveys could manage. (news.ucr.edu) ### How big is this map, exactly? COSMOS-Web covered a contiguous patch of sky about the size of three full Moons, according to the project team and UC Riverside. For JWST, which is often used for very deep but narrower observations, that makes COSMOS-Web the largest General Observer program selected for the telescope. The project’s overview page says the survey used 255 hours of observing time and mapped a 0.6 square-degree area with deep NIRCam imaging, plus a separate 0.2 square-degree area with MIRI in parallel. (news.ucr.edu) Hossein Hatamnia, a UC Riverside graduate student and the study’s lead author, said COSMOS-Web was designed “from the start” to provide the wide and deep view needed to see the cosmic web. RIT’s Jeyhan Kartaltepe, a COSMOS co-leader and study co-author, said the survey was built to trace the evolution of structure over the age of the universe using JWST’s sensitivity and resolution. (news.ucr.edu) ### What does “164,000 galaxies” actually mean here? The new map is not 164,000 galaxies in a single flat image. The underlying paper says the researchers reconstructed large-scale structure using roughly 160,000 galaxies with robust photometric redshifts, placing each galaxy at an estimated distance and time in cosmic history. In the team’s visualizations, the present day sits at one end and earlier epochs extend outward, letting astronomers trace how dense regions and voids change over time. (news.ucr.edu) UC Riverside said the reconstruction follows the network of galaxies back to when the universe was about 1 billion years old. RIT described the released product as one of the cleanest and most reliable reconstructions yet of large-scale structure, and said the public materials include the galaxy catalog, the map-building pipeline and a video of the web evolving across billions of years. (iopscience.iop.org) ### What is the “cosmic web” scientists are trying to see? The cosmic web is the universe’s large-scale framework of filaments, sheets and dense nodes, shaped largely by dark matter and gas, with galaxies collecting along those structures. Astronomers cannot directly photograph dark matter, so they infer the web by mapping where galaxies sit and how densely they cluster. The better the galaxy census and the more accurate the distances, the sharper that reconstruction becomes. (news.ucr.edu) The Astrophysical Journal paper says the COSMOS-Web reconstruction was used to trace galaxy evolution in different environments up to redshift 7. That lets researchers compare galaxies in dense regions with those in sparser ones over much of cosmic time, rather than only in the nearby universe. ### Why did JWST make this possible when earlier surveys struggled? (news.ucr.edu) JWST’s infrared instruments can detect faint, distant galaxies that were difficult or impossible for earlier observatories to see, especially in the dusty and very early universe. UC Riverside said that sensitivity and sharpness let COSMOS-Web push the map back to epochs that older wide-area reconstructions could not resolve as clearly. (iopscience.iop.org) The project page says COSMOS-Web was designed not only to map large-scale structure but also to expand the census of galaxies from the epoch of reionization and track the evolution of massive galaxies across a broad redshift range. In practice, that means the same survey can support both headline visuals and a large archive of follow-on studies. ### What happens next? (news.ucr.edu) The study, titled “Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to z ∼ 7 with the Largest JWST Survey,” has been published in The Astrophysical Journal. COSMOS-Web and affiliated institutions say the map products, galaxy catalog and processing pipeline are now public, giving other researchers material to test models of galaxy formation and large-scale structure with the same data set. (cosmos.astro.caltech.edu) (iopscience.iop.org)