First images released from James Webb Space Telescope’s largest general observer program

Mosaic images from the COSMOS-Web program offer a treasure trove of early galaxies

four galaxy images
Four galaxies from the first epoch of COSMOS-Web NIRCam observations highlight a range of structures: a barred spiral galaxy (top left); a gravitational lens (top right), where the mass of the central galaxy is causing the light from a distant galaxy to be stretched into arcs; a nearby galaxy displaying shells of material, suggesting it merged with another galaxy in its past (lower left); a barred spiral galaxy with several clumps of active star formation (lower right). (Image credit: COSMOS-Web/Kartaltepe/Casey/Franco/Larson/RIT/UT Austin/CANDIDE.)
galaxy images
The first COSMOS-Web NIRCam observations cover six visits or pointings out of a total of 152 planned visits. The relative position of this mosaic in the survey is shown at upper left. At lower left are several zoomed-in cutouts showing individual galaxies selected from these first data. (Image credit: COSMOS-Web/Kartaltepe/Casey/Franco/Larson/RIT/UT Austin/CANDIDE.)

The first images from the largest program in the James Webb Space Telescope’s first year show many types of galaxies, including dazzling examples of spiral galaxies, gravitational lensing, and evidence of galaxy mergers. Scientists from the COSMOS-Web program have released mosaic images taken in early January by JWST’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

COSMOS-Web aims to map the earliest structures of the universe and will create a wide and deep survey of up to 1 million galaxies. Over the course of 255 hours of observing time, COSMOS-Web will map 0.6 square degrees of the sky with NIRCam, roughly the size of three full moons, and 0.2 square degrees with MIRI.

“COSMOS-Web provides an unparalleled, wide-angle view of the distant universe with JWST,” said Brant Robertson, professor of astronomy and astrophysics at UC Santa Cruz and a member of the COSMOS-Web Management Committee. "By surveying such a large area on the sky, we can finally begin to untangle how the formation of galaxies is influenced by their cosmic environments.”

COSMOS-Web has three primary science goals: furthering our understanding of the Reionization Era, roughly 200,000 to 1 billion years after the Big Bang; identifying and characterizing early massive galaxies in the first two billion years; and studying how dark matter has evolved with the stellar content of galaxies. COSMOS-Web is the widest area JWST will observe in its first year, enabling the study of galaxies across a wide range of local environments. The images taken so far show incredible detail when compared with those taken previously by other observatories such as the Hubble Space Telescope and Spitzer Space Telescope.

“It’s incredibly exciting to get the first data from the telescope for COSMOS-Web,” said principal investigator Jeyhan Kartaltepe, an associate professor at Rochester Institute of Technology. “Everything worked beautifully, and the data are even better than we expected. We’ve been working really hard to produce science quality images to use for our analysis and this is just a drop in the bucket of what’s to come.”

The mosaics were created from six pointings of the telescope taken January 5 and 6. The telescope will take 77 pointings, roughly half the field, in April, and the remaining 69 pointings are scheduled to take place in December 2023 and January 2024.

“JWST has delivered such stunning images of this region that sources are literally popping out in every small patch of the observed sky,” said Santosh Harish, a postdoctoral research associate at RIT. “What were thought to be compact objects based on the best images we had so far, the JWST observations are now able to resolve these objects into multiple components, and in some cases even reveal the complex morphology of these extragalactic sources. With these first observations, we have just barely scratched the surface of what is to come with the completion of this program, next year.”

An overview of COSMOS-Web’s survey design, implementation, and outlook is available on ArXiv. Additional information, including downloadable high-resolution images taken for the COSMOS-Web program, is available on the COSMOS website at