A young galaxy with the catchy and improvised name A1689-zD1 has galactic formation experts talking. Recent observations show that this galaxy, as it would have appeared just 700 million years after the Big Bang, is larger than originally thought, with significant outflows of hot gas from its core and a halo of cold gas emanating from its outer edge. A1689-zD1 is considered representative of young “normal” galaxies (as opposed to “massive” galaxies), and the new observations suggest that the adolescence of normal galaxies may be more exuberant than previous models suggest.
A1689-zD1 was first observed in 2007 by the Hubble Space Telescope, and at the time it was a contender for the most distant galaxy ever discovered (a record that has been broken multiple times, most recently in April 2022). Indeed, it is so distant that the only reason it is possible to get such a good view of it is because it is conveniently located behind a much closer galaxy, whose gravitational interaction with spacetime creates a lens effect, magnifying the distant A1689-zD1 behind. The Spitzer Space Telescope was able to observe the galaxy alongside Hubble, but the clearest images of the galaxy were obtained within the Atacama Large Millimeter/submillimeter Array (ALMA), which specializes in wavelengths invisible to the naked eye and well adapted to extremely distant objects. .
The ALMA data tells a story buried in the details that Hubble and Spitzer couldn’t see.
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“The emission of carbon dioxide in A1689-zD1 is much more extensive than what has been observed with the Hubble Space Telescope”, explains Seiji Fujimoto, postdoctoral researcher at the Niels Bohr Institute, “and this could mean that the first galaxies are not as small as they appear. If, in fact, the first galaxies are larger than we previously thought, it would have a major impact on the theory of galaxy formation and evolution in the universe. primitive universe.
Along with the startling circumference of A1689-zD1, it also appears to be undergoing a surprisingly high level of star formation in a halo of carbon dioxide surrounding the galaxy, although this gas could also be a sign of a galactic merger that is occurring. occurred during the early stages of galaxy formation. Either way, it suggests a surprisingly dynamic early phase of galaxy formation.
Closer to the galaxy’s core, the team also observed signs of hot, ionized gas that typically represent extreme energetic events such as supernova explosions or powerful jets from a black hole’s accretion disk. This hot gas outflow may be related to the cold gas halo further on, and intrigued the researchers. At the very least, they didn’t expect to see him in such a young galaxy. “We’ve seen this type of extended gas halo emission from galaxies that formed later in the Universe, but seeing it in such an old galaxy means this type of behavior is universal even in smaller galaxies. which formed most of the stars in the early universe,” says Darach Watson, associate professor at the Niels Bohr Institute. “Understanding how these processes occurred in such a young galaxy is critical to understanding how the formation of ‘Stars Occurred in the Early Universe.’
Of course, this observation alone is not likely to rewrite the textbooks just yet. Researchers will continue to observe the early universe for galaxies of similar age, to determine whether A1689-zD1 is typical in size and activity, or an outlier.
The James Webb Space Telescope, which like ALMA is well suited to observing young galaxies at this distance, should soon provide a larger sample to study. it is ready to go live later this summer – although it will also rely on fortuitous gravitational lensing to find and study early galaxies.
Featured Image: Artist’s conception of the A1689-zD1. Extending well beyond the center of the galaxy, shown here in pink, is an abundant halo of cold carbon dioxide. For scientists, this unusual feature indicates that the galaxy may be much larger than previously believed and that the early stages of normal galaxy formation may have been more active and dynamic than expected. At top left and bottom right are outflows of hot, ionized gas pushing outward from the center of the galaxy, shown here in red. Scientists think it’s possible that these outflows have something to do, although they don’t yet know what, with the presence of cold carbon dioxide in the outer reaches of the galaxy. Credit: ALMA (ESO/NAOJ/NRAO), B. Saxton (NRAO/AUI/NSF)
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