These galaxies appear to provide a missing evolutionary step that links ultradistant, extremely bright galaxies observed at around 13.3 billion years ago with massive, quiescent systems that had already stopped forming stars roughly 2 billion years after the Big Bang.
The discovery, published in The Astrophysical Journal Letters, suggests that current cosmological models underestimate how early and how efficiently stars formed in the young universe.
Jorge Zavala, assistant professor of astronomy at UMass Amherst and lead author of the paper, has long focused on a rare class of dusty, star-forming galaxies first identified in the late 1990s, but their heavy dust content has made them difficult to study with traditional telescopes.
Dust in these systems absorbs ultraviolet and visible light, leaving them effectively invisible to instruments that operate mainly in those parts of the spectrum and obscuring key stages in galaxy growth.
The advent of submillimeter observatories changed that picture by opening a window onto longer-wavelength emission, where dust-reprocessed radiation from star formation emerges as infrared and submillimeter light.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, Zavala and colleagues first assembled a catalog of about 400 bright, dusty galaxies, providing a foundation for searching even fainter, more distant populations.
They then combined those data with near-infrared observations from NASA's James Webb Space Telescope, which allowed the team to isolate about 70 faint dusty galaxy candidates close to the edge of the observable universe, most of which had not been detected previously.
By stacking the ALMA observations at the positions of these candidates, the astronomers were able to confirm that they are indeed dusty, star-forming galaxies seen as they existed almost 13 billion years ago.
The analysis shows that these galaxies are both massive and rich in metals and cosmic dust, implying that generations of stars had already lived and died by this early epoch.
According to Zavala, the existence of such evolved, dust-rich systems so soon after the Big Bang indicates that star formation must have started earlier, and proceeded more rapidly, than standard models predict for the early universe.
The newly studied population also appears to be connected to two other rare galaxy classes: ultrabright, star-forming galaxies that JWST has recently identified shortly after the Big Bang, and older, massive quiescent galaxies that have largely ceased forming stars by about 2 billion years after the universe began.
Taken together, these three groups of objects may outline a lifecycle in which ultrabright systems represent the early growth phase, the newly identified dusty galaxies mark a more mature, still vigorously star-forming stage, and the quiescent galaxies correspond to the final, inactive phase.
If this evolutionary sequence is confirmed by future work, it will imply that widely used models of galaxy formation and evolution are missing important physical processes in the first few billion years of cosmic history.
The study underscores how rapidly new facilities are reshaping the view of the distant universe, and how combining data from complementary observatories such as ALMA and JWST can reveal populations that were previously hidden.
Zavala emphasized that the project depended on close collaboration among researchers and institutions around the globe, supported in part by funding from the U.S. National Science Foundation.
Research Report:ALMA and JWST Identification of Faint Dusty Star-forming Galaxies up to z ~ 8 and Their Connection with Other Galaxy Populations
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University of Massachusetts Amherst
Understanding Time and Space
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