One of the design goals of the James Webb Space Telescope was to provide the ability to generate images at wavelengths that would reveal the first stars and galaxies in the Universe. Now, just a few weeks after its first images were revealed, we have a strong indication that it’s a hit. In some of the data that NASA has made public, researchers have detected up to five galaxies in the distant Universe, already present only a few hundred million years after the Big Bang. If they are confirmed to be as distant as they seem, one of them will be the most distant galaxy observed so far.
Opening
For many of its observatories, NASA allows astronomers to submit observing proposals and allows those users exclusive access to the resulting data at a later time. But for its newest instrument, NASA has a set of goals where the data will be made public immediately, for anyone to analyze as they wish. Some of these include locations similar to one of the first images publishedwhere a large foreground galaxy cluster acts as a lens to magnify more distant objects.
(You can see the details of one of the datasets used for this analysiscalled GLASS, which used the Abell 2744 cluster to magnify distant objects, which were further magnified by the telescope).
The images in this dataset were long exposures made in different parts of the infrared spectrum. The entire range of wavelengths covered by the NIRCam instrument was divided into seven parts, and each part was imaged for 1.5 to 6.6 hours. A large international team of researchers used these fragments to perform an analysis that would help them identify distant galaxies by looking for objects that were present in some parts of the spectrum but missing in others.
The search was based on the understanding that most of the Universe was filled with hydrogen atoms for hundreds of millions of years after the formation of the Cosmic Microwave Background. These would absorb any light at or above a wavelength that was sufficient to ionize hydrogen, essentially making the Universe opaque at these wavelengths. At the time, this cutoff was somewhere on the ultraviolet end of the spectrum. But in the intervening time, the expansion of the Universe shifted that cutoff into the infrared portion of the spectrum, one of the key reasons Webb was designed to be sensitive to these wavelengths.
First you don’t see it (left), then you see it. The brightness of the inverted images shows an object appearing in a region of space highlighted by a cross, but only at longer wavelengths.
So the team looked for objects that were present in the images of the lower energy fragments of the infrared spectrum imaged by Webb but absent in the higher energy fragments. And the precise point at which it disappeared indicates how far redshifted the boundary is for that galaxy, and thus how distant the galaxy is. (You can expect future research to involve a similar approach.)
This method produced five different objects of interest, and a draft manuscript focuses on the two most distant: GLASS-z13 and GLASS-z11. The former is even more distant than the farthest confirmed distance of anything seen in the Hubble Deep Field; if confirmed, this would make it the most distant object we know of, and therefore the closest in time to the Big Bang.
