NASA’s new toy may have already discovered the oldest known galaxy

NASA’s new toy may have already discovered the oldest known galaxy

Two nearly spherical and heavily pixelated objects.
Enlarge / The two newly imaged galaxies, the older one on the right.

One of the design goals for the James Webb Space Telescope was to provide the ability to provide images at wavelengths that would reveal the Universe’s first stars and galaxies. Now, just weeks after the first images were revealed, we’re getting a strong indication that it’s a success. In some of the data released by NASA, researchers have spotted up to five galaxies from the distant Universe that exist as early as a few hundred million years after the Big Bang. If they are confirmed to be as distant as they appear, one of them will be the most distant galaxy yet observed.

Open

For many of its observatories, NASA allows astronomers to submit observation proposals and gives those users exclusive access to the resulting data for a time thereafter. But for its newest instrument, NASA has a set of targets where the data will be released immediately for anyone to analyze at their leisure. Some of these contain locations resembling one of the first images released, where a large foreground galaxy cluster acts as a lens to magnify more distant objects.

(You can look at the details of one of the datasets used for this analysis called GLASS, which used the Abell 2744 cluster to magnify distant objects further magnified by the telescope.)

The images in this dataset were long exposures taken at different portions of the infrared spectrum. The entire wavelength range covered by the NIRCam instrument was divided into seven sections and each section was imaged for between 1.5 and 6.6 hours. A large international team of researchers used these chunks 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 absent in others.

The search was based on the understanding that most of the universe was filled with hydrogen atoms hundreds of millions of years after the cosmic microwave background formed. These would absorb any light at or above a wavelength sufficient to ionize the hydrogen, essentially rendering the universe opaque to those wavelengths. At the time, that cutoff was somewhere in the UV end of the spectrum. But in the meantime, the expansion of the universe pushed that frontier into the infrared portion of the spectrum — one of the main reasons the Webb was engineered to be sensitive to these wavelengths.

First you don't see it (left), then you do.  Inverted brightness images show an object appearing in an area of ​​space highlighted by a crosshair, but only at longer wavelengths.

First you don’t see it (left), then you do. Inverted brightness images show an object appearing in an area of ​​space highlighted by a crosshair, but only at longer wavelengths.

So the team looked for objects that were present in Webb’s images of the lowest energy chunks of the infrared spectrum but were absent from the higher energy chunks. And the exact point at which it disappeared indicates how redshifted the cutoff is for that galaxy and therefore how far away the galaxy is. (You can expect future research to take a similar approach.)

This method yielded five distinct objects of interest, and a draft manuscript focuses on the two most distant: GLASS-z13 and GLASS-z11. The former is even further away than the furthest confirmed distance of anything seen in the Hubble Deep Field; If confirmed, it would be the most distant object we know of, and thus the closest in time to the Big Bang.

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