One of the major aims of the James Webb Space Telescope is to observe some of the earliest galaxies in the universe, and to do that it needs to be able to see extremely distant objects. But looking at a particular very old galaxy in detail is only half of the problem. To truly understand the earliest stages of the universe, astronomers also need to see how these very old galaxies are distributed so they can understand the large-scale structure of the universe.
That’s the aim of the COSMOS-Web program, which is using James Webb to survey a wide area of the sky and look for these rare, ancient galaxies. It aims to study up to 1 million galaxies during over 255 hours of observing time, using both Webb’s near-infrared camera (NIRCam) and its mid-infrared instrument (MIRI) camera. While there is still plenty of observing left to do, the researchers in the COSMOS-Web program recently shared some of their first results.
“It’s incredibly exciting to get the first data from the telescope for COSMOS-Web,” said principal investigator Jeyhan Kartaltepe of the Rochester Institute of Technology, in a statement. “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 first images include four galaxies, chosen because they represent the different types of galaxy that the survey will find. There is a barred spiral galaxy, like our Milky Way, and a similar galaxy undergoing vigorous star formation. There is also a galaxy that seems to have recently merged, and one galaxy whose light is bent due to gravitational lensing.
These are just a tiny slice of the galaxies identified by the survey so far. The image above shows the observations taken between January 5 and 6 this year, giving an indication of just how big and detailed the eventual full survey will be. This mosaic was made up of six pointings by the telescope, out of a total of 77 to be made in April and May this year, with a further 69 coming in December 2023 and January 2024.
“This first snapshot of COSMOS-Web contains about 25,000 galaxies — an astonishing number larger than even what sits in the Hubble Ultra Deep Field,” said principal investigator Caitlin Casey of the University of Texas at Austin. “It’s one of the largest JWST images taken so far. And yet it’s just 4% of the data we will get for the full survey. When it is finished, this deep field will be astoundingly large and overwhelmingly beautiful.”