A week later, astronomers discover a galaxy even deeper in time

Enlarge / The James Webb Space Telescope continues to deliver on its promise of discovering the first galaxies.


Data from the Webb Space Telescope has only been in the hands of astronomers for the past few weeks, but they’ve been waiting for this for years and apparently have analyzes underway. The result has been something like a race in time, as new discoveries find objects that formed closer and closer to the Big Bang that produced our Universe. Last week, one such search revealed a galaxy that was present less than 400 million years after the Big Bang. This week, a new scan has identified a galaxy as it appeared just 233 million years after the birth of the Universe.

This discovery is a happy by-product of work that was designed to answer a larger question: how many galaxies should we expect to see at different times after the Big Bang?

In time

As we mentioned last week, the early Universe was opaque to light at all wavelengths that carry more energy than is needed to ionize hydrogen. This energy is in the UV part of the spectrum, but the redshift caused by 13 billion years of an expanding Universe has moved this cutoff point into the infrared part of the spectrum. To find galaxies from this era, we need to look for objects that are not visible at shorter infrared wavelengths (meaning the light was once above the hydrogen threshold), but appear at lower energy wavelengths.

The deeper the border between the invisible and the visible is in the infrared, the stronger the redshift and the further away the object is. The further away the object, the closer in time it is to the Big Bang.

Studies of these galaxies can tell us something about their individual properties. But identifying a large collection of early galaxies can help us determine how quickly they formed and identify any changes in galaxy dynamics that occurred at a specific time in the Universe’s past. . This change over time in the frequency of visible objects is called a “luminosity function”, and work has been done to characterize the luminosity function of early galaxies. But the infrared wavelengths of the first galaxies are absorbed by the Earth’s atmosphere and therefore must be imaged from space. And that was one of the design goals of the Webb telescope.

The new work has focused on examining the luminosity function of galaxies that formed shortly (in astronomical terms) after the Big Bang. But, by generating a catalog of early galaxies, the researchers spot what appears to be the oldest galaxy ever photographed.

Definition of the function

The researchers used two data sources to reconstruct the appearances of galaxies at different times. One was produced by analyzing work done with a ground-based infrared telescope (ESA’s VISTA telescope) and the Spitzer Space Telescope, both of which photographed galaxies that were relatively older when they produced the light that is now reaching Earth – some 600 million years or more after the Big Bang. The other involved data generated by the Webb, including the datasets analyzed in the article we reported on and an imaged area in the first public photo release. In all cases, the researchers looked for the same thing: objects present at longer infrared wavelengths but absent at shorter wavelengths.

In total, the team identified 55 distant galaxies, 44 of which had never been noted before. Thirty-nine of them come from Webb’s data, and that figure included the two ancient galaxies that were identified last week. The numbers aren’t particularly accurate at higher redshifts, where they’re based on just one or two galaxies. But overall, the trend suggests a gradual decline in visible objects up to a few hundred million years from the Big Bang, with no abrupt changes or breaks.

But what is striking is that there is data for a galaxy at an extremely large redshift (z=16.7, for those who understand these things). This places it less than 250 million years after the Big Bang. This distance is based in part on the fact that the first wavelength filter the object appears in shows it to be very faint there, suggesting it is faint at the wavelengths the filter leaves behind. pass. This suggests that the light cutoff generated by hydrogen is near the edge of the filter range.

Like the distant galaxies described last week, it also appears to have a billion suns’ worth of matter in the form of stars. Researchers estimate that it could have started star formation as early as 120 million years after the Big Bang, and certainly did so around 220 million years ago.

The researchers are quite confident that this new galaxy represents a genuine discovery: “After extensive research, we are currently unable to find a plausible explanation for this object, other than a galaxy at a new redshift record.” And by adding a second independent confirmation of previous galaxy discoveries, it greatly increases the confidence we have in those discoveries. All of this indicates that the new telescope is delivering on its promise, at least when it comes to early galaxies.

The big question now is what will happen when pointed at high-lens areas, which might be able to magnify objects to a point where we can image structures within these early galaxies. It is possible that we have already done this, but we will have to wait for the descriptions to appear on the arXiv.

The arXiv. Abstract number: 2207.12356 (About arXiv).

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