JWST COSMOS-Web maps 164,000 galaxies

On May 11, researchers led by the University of California, Riverside said they had used NASA’s James Webb Space Telescope to assemble what they described as the most detailed map yet of the universe’s cosmic web. The reconstruction draws on the COSMOS-Web survey, the largest JWST survey so far, and traces the distribution of galaxies across 13.7 billion years of cosmic history. The team said the work is based on roughly 164,000 galaxies and reaches back to a time when the universe was about 1 billion years old. The study appears in *The Astrophysical Journal*. ### How did the team build this map from JWST data? The COSMOS-Web survey was designed as a wide-field JWST program covering a contiguous 0.6 square degree area with deep near-infrared imaging, according to the project overview. The survey builds on the long-running COSMOS field and was set up to study galaxy formation and large-scale structure across cosmic time. Hossein Hatamnia, a graduate student at UC Riverside and Carnegie Observatories and the paper’s lead author, said the team used COSMOS-Web to get the “wide, deep view” needed to see the cosmic web. The paper says the reconstruction used a weighted kernel density estimation method applied to about 160,000 galaxies with robust photometric redshifts, while university release materials described the public map and catalog as covering about 164,000 galaxies. (cosmos.astro.caltech.edu) ### What exactly is the “cosmic web” the map is showing? The cosmic web is the large-scale arrangement of matter in the universe, with galaxies gathering along filaments and sheets around relatively empty voids, the researchers said. The UC Riverside release described it as the underlying architecture linking galaxies and clusters across immense distances. The new reconstruction places galaxies by cosmic time, with dense regions and filaments highlighted against darker, emptier regions. (eurekalert.org) The release said the map reaches from the nearby universe back to epochs when the universe was less than a billion years old. ### Why does COSMOS-Web matter more than earlier maps of the same field? Bahram Mobasher, a physics and astronomy professor at UC Riverside and a co-author, said the large-scale structure identified from the JWST data is more informative than earlier maps of the same sky region taken with the Hubble Space Telescope. (eurekalert.org) JWST’s infrared sensitivity allows it to detect faint, distant galaxies that earlier observatories could not see as clearly, according to the paper and project materials. The paper’s title says the map traces galaxy evolution in the cosmic web up to about redshift 7. In astronomy, that corresponds to very early epochs, and the team said the survey was built to follow how environment shaped galaxies from the epoch of reionization toward the present day. ### What did the researchers say the map could be used for next? Hatamnia said the dataset allows researchers to study galaxy evolution in cluster and filament structures across cosmic time. (eurekalert.org) The COSMOS-Web overview says one of the survey’s main goals is to constrain how massive galaxies formed and evolved in the universe’s first two billion years. The paper and release materials frame the reconstruction as a tool for testing how galaxy properties depend on environment. (iopscience.iop.org) That includes comparing observed structures and galaxy populations with theoretical models and simulations, according to the authors’ description of the project’s science goals. ### Where can other researchers look at the results now? The COSMOS collaboration’s website lists COSMOS-Web as a 255-hour JWST Cycle 1 treasury program and provides project information, including the survey overview and principal investigators Jeyhan Kartaltepe and Caitlin Casey. (eurekalert.org) The team has also said the map products, catalog and analysis pipeline have been released publicly. The paper, titled “Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to z ∼ 7 with the Largest JWST Survey,” is published by the American Astronomical Society in *The Astrophysical Journal*. (arxiv.org) The public release materials say researchers can access the map products and supporting files through COSMOS-Web release channels tied to the survey. (iopscience.iop.org) (cosmos.astro.caltech.edu)