NASA
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 it for years, and the analysis is probably already in the works. The result has been something of a race backwards through time, with new discoveries finding objects ever closer to the Big Bang that created our Universe. last week, this is one of the quests A galaxy has emerged that exists 400 million years after the Big Bang. A new analysis this week singled out a galaxy that appeared just 233 million years after the universe began.
The discovery is the welcome product of work designed to answer a more general question: How many galaxies should we expect to see at various points in time after the Big Bang?
back in time
As we noted last week, the early Universe was opaque to light at any wavelengths carrying more energy than needed to ionize hydrogen. This energy is in the UV part of the spectrum, but the 13 billion year redshift caused by the expanding Universe has shifted this cutoff point to the infrared part of the spectrum. To find galaxies from this time on, we must look for objects that are invisible at shorter infrared wavelengths (meaning the light was once above the hydrogen cutoff), but are visible at lower-energy wavelengths.
The deeper the boundary between the invisible and the visible is into the infrared, the stronger the redshift and the more distant the object. The more distant the object, the closer in time it is to the Big Bang.
Studying 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 galactic dynamics at some point in the Universe’s past. This change in the frequency of visible objects over time is called the “luminosity function,” and some work has been done to characterize the luminosity function of early galaxies. But the infrared wavelengths of the earliest galaxies are absorbed by Earth’s atmosphere and must therefore be imaged from space. This was one of the design goals of the Webb Telescope.
The new work is focused on studying the luminosity function of galaxies formed shortly after (in astronomical terms) the Big Bang. However, researchers cataloging the first galaxies are discovering what appear to be the oldest galaxies ever imaged.
Defining a function
The researchers used two sources of data to reconstruct the appearance of the galaxies at different times. One of them is a ground-based infrared telescope (ESA’s VIEW telescope) and the Spitzer space telescope, both of which imaged galaxies that were relatively old when they produced the light that reached Earth about 600 million years or more after the Big Bang. Other data generated by Webb, including datasets analyzed in the paper we have given information about and an area described first public photo release. In all cases, the researchers were looking for the same thing: objects that exist at longer infrared wavelengths but not at shorter ones.
In total, the team identified 55 distant galaxies, 44 of which had not been observed before. Of those, 39 come from Webb data, and that number includes two ancient galaxies identified last week. The numbers are particularly imprecise at high redshifts, where they are based on only one or two galaxies. But overall, the trend suggests a gradual decline in visible objects over the several hundred million years since the Big Bang, without sharp changes or discontinuities.
But what’s interesting is that there is data for galaxies at extremely high redshift (z = 16.7, for those who understand). This puts it less than 250 million years after the Big Bang. This distance is based in part on the fact that the first wavelength filter at which the object is seen shows that it is very faint there, indicating that the filter is weak at the wavelengths it passes. This indicates that the light cutoff caused by hydrogen is near the edge of the filter band.
Like the distant galaxies imaged last week, it appears to contain a billion Suns worth of material in the form of stars. Researchers believe it may have started forming stars 120 million years after the Big Bang, and certainly did so for 220 million years.
The researchers are quite confident that this new galaxy is a real find: “At this time, we cannot find any plausible explanation for this object other than a galaxy with a redshift record.” And by adding a second independent confirmation of previous galaxy findings, it greatly increases our confidence in these discoveries. All this suggests that the new telescope is delivering as promised, at least in terms of the first galaxies.
The key question now is what will emerge when objects are focused into highly lensed fields that can magnify the structures in these early galaxies to the point where we can image them. It is possible that we have already done this, but we will have to wait for the images to appear in arXiv.
arXiv. Abstract number: 2207.12356 (About arXiv).
