Researchers analyzing images from the James Webb Space Telescope report 300 unusually bright objects that vanish from bluer filters yet appear in redder ones, a classic signature used to flag very distant systems.
Some of these sources almost certainly belong to a closer crowd wearing heavy dust. Others could sit far back in cosmic time, where our current playbook for how galaxies grow gets stressed.
The research was led by Liu Bangzheng “Tom” Sun and Haojing Yan in the Department of Physics and Astronomy at the University of Missouri (UM).
JWST finds 300 bright objects
The study sifted public JWST images across four deep fields and cataloged 300 very bright “dropouts,” then focused on 137 objects that also have mid infrared measurements, a combination that helps rule in or rule out distant candidates.
Their modeling shows that most of these luminous dropouts are nearby in cosmic terms, likely at redshift z ≈ 1–4, while a nontrivial slice could be truly distant at z greater than 6, a mix that demands careful follow up.
“These mysterious objects are candidate galaxies in the early universe, meaning they could be very early galaxies,” said Haojing Yan, co-author of the study.
Redshift and early galaxies
As light travels for billions of years, its wavelength stretches to the red end of the spectrum, a shift that pushes early galaxies out of optical reach and into the infrared.
JWST’s Near Infrared Camera, NIRCam, is purpose built for that stretch to observe redshifts and sees from 0.6 to 5.0 microns.
The Mid Infrared Instrument (MIRI) extends that reach to roughly 5 to 28 microns, giving astronomers an extra set of eyes that can be decisive when red colors come from dust instead of distance.
The broader context is moving quickly. Spectroscopy with JWST has now been locked in galaxies beyond redshift 14, showing that luminous systems were present only about 290 million years after the Big Bang.
“As the light from these early galaxies travels through space, it stretches into longer wavelengths, shifting from visible light into infrared,” said Yan, explaining redshift.
High-redshift dropout technique
The team used the “dropout technique,” which flags an abrupt loss of flux blueward of the Lyman break and a clear detection just redward of that break, a method pioneered in the 1990s and refined ever since.
“It detects high-redshift galaxies by looking for objects that appear in redder wavelengths but vanish in bluer ones,” said Bangzheng “Tom” Sun, referring to the dropout signature tied to absorption by neutral hydrogen.
Color cuts are only the start. The team estimated photometric redshifts using three independent spectral energy distribution fitting tools, including Le Phare and EAZY, to weigh high redshift solutions against dusty, lower redshift impostors.
Spectroscopy remains the gold standard. It breaks a galaxy’s light into its component wavelengths and nails down spectroscopic redshift when emission lines are identified, which is why the authors call for more follow up.
One extreme bright galaxy
Among the sample sits a known source in the CEERS field at redshift z = 8.68, originally identified from ground based Keck data because its infrared color hinted at strong oxygen emission, then studied repeatedly with JWST.
Later observations revealed active black hole signatures in the same redshift neighborhood, including broad H beta emission that points to an accreting nucleus embedded in a vigorously star forming host.
That kind of source shows how a single, very bright object can be luminous for multiple reasons, from intense star formation to an active nucleus, and why mid infrared measurements help disentangle the power sources.
Early galaxies and high-redshift
The headline is not that every bright dropout is ancient, but that some probably are, and the brightest of those could stress current models if confirmed.
Theoretical work has shown that it is possible to reproduce many luminous early galaxies by dialing up star formation efficiency in massive halos at high density, yet the very brightest systems remain a challenge.
“Even if only a few of these objects are confirmed to be in the early universe, they will force us to modify the existing theories of galaxy formation,” said Yan.
Sun and Yan emphasize that spectroscopy will deliver the final word, since dusty galaxies at modest redshift can mimic the same colors that signal extreme distance.
That caution is well placed, given how often the Lyman break can be confused with a strong Balmer break in redder, older systems.
The study is published in The Astrophysical Journal.
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