Over the last two years, scientists have utilized NASA’s James Webb Space Telescope (JWST) to explore what astronomers call Cosmic Dawn, the period in the first few hundred million years after the Big Bang when the first galaxies formed. These early galaxies provide crucial insights into the evolution of gas, stars, and black holes during the universe's infancy. In October 2023 and January 2024, an international team of astronomers employed Webb to observe galaxies as part of the JWST Advanced Deep Extragalactic Survey (JADES) program. Using Webb’s Near-Infrared Spectrograph (NIRSpec), they captured a spectrum of a record-breaking galaxy observed only 290 million years after the Big Bang.
This corresponds to a redshift of about 14, indicating how much the galaxy's light has been stretched by the universe's expansion. Stefano Carniani from Scuola Normale Superiore in Pisa, Italy, and Kevin Hainline from the University of Arizona in Tucson, Arizona, were invited to explain how this galaxy was found and what its unique characteristics reveal about galaxy formation.
The instruments on Webb were designed to detect and understand the earliest galaxies. During the first year of observations for the JWST Advanced Deep Extragalactic Survey (JADES), we identified many hundreds of candidate galaxies from the first 650 million years after the Big Bang. In early 2023, we discovered a galaxy in our data that showed strong evidence of being above a redshift of 14, which was incredibly exciting. However, certain properties of the source gave us pause. The galaxy was surprisingly bright for such a distant object and was located very close to another galaxy, making them appear as a single larger entity.
When we observed the source again in October 2023, as part of the JADES Origins Field, new imaging data from Webb’s narrower Near-Infrared Camera (NIRCam) filters further supported the high-redshift hypothesis. We realized that obtaining a spectrum was crucial, as any findings would be of immense scientific significance—either marking a new milestone in Webb’s exploration of the early universe or presenting a perplexing anomaly of a middle-aged galaxy.
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| This infrared image from NASA’s James Webb Space Telescope (JWST) was taken by the Near-Infrared Camera (NIRCam) for the JWST Advanced Deep Extragalactic Survey (JADES) program. The NIRCam data helped identify galaxies for further study with spectroscopic observations. One such galaxy, JADES-GS-z14-0 (shown in the pullout), was determined to be at a redshift of 14.32 (+0.08/-0.20), making it the current record-holder for the most distant known galaxy, corresponding to a time less than 300 million years after the Big Bang. In the background image, blue represents light at 0.9, 1.15, and 1.5 microns (filters F090W, F115W, and F150W), green is 2.0 and 2.77 microns (F200W and F277W), and red is 3.56, 4.1, and 4.44 microns (F356W, F410M, and F444W). The pullout image shows light at 0.9 and 1.15 microns (F090W and F115W) as blue, 1.5 and 2.0 microns (F150W and F200W) as green, and 2.77 microns (F277W) as red. |
In January 2024, NIRSpec observed the galaxy JADES-GS-z14-0 for nearly ten hours, and when the spectrum was first processed, there was unambiguous evidence that the galaxy was at a redshift of 14.32, shattering the previous record held by JADES-GS-z13-0 (z = 13.2). This discovery was incredibly exciting for the entire team, given the mystery surrounding the source. The significance of JADES-GS-z14-0 lies not just in setting a new distance record; at this distance, the galaxy must be intrinsically very luminous.
The images show that the galaxy spans over 1,600 light-years, indicating that the light primarily comes from young stars rather than from emission near a growing supermassive black hole. The amount of starlight suggests the galaxy's mass is several hundred million times that of the Sun. This raises the intriguing question: How can nature create such a bright, massive, and large galaxy in less than 300 million years?
The data reveal other critical aspects of this astonishing galaxy. The galaxy’s color is not as blue as expected, indicating some of the light is reddened by dust, even at these early times. JADES researcher Jake Helton from Steward Observatory and the University of Arizona also identified that JADES-GS-z14-0 was detected at longer wavelengths with Webb’s Mid-Infrared Instrument (MIRI), a remarkable feat given its distance. The MIRI observation covers wavelengths that were emitted in the visible-light range but redshifted beyond the reach of Webb’s near-infrared instruments.
Jake’s analysis indicates that the brightness implied by the MIRI observation exceeds what would be expected from other Webb instruments' measurements, suggesting the presence of strong ionized gas emission from hydrogen and oxygen. The presence of oxygen so early in the galaxy’s history is surprising and suggests that multiple generations of very massive stars had already lived and died by the time we observed the galaxy.
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| Scientists used NASA’s James Webb Space Telescope’s NIRSpec (Near-Infrared Spectrograph) to obtain a spectrum of the distant galaxy JADES-GS-z14-0, accurately measuring its redshift to determine its age. The redshift, determined from the Lyman-alpha break, indicates this galaxy dates back to less than 300 million years after the Big Bang. |
All these observations indicate that JADES-GS-z14-0 differs significantly from the types of galaxies predicted by theoretical models and computer simulations to exist in the very early universe. Given the source's brightness, we can predict its growth over cosmic time, and so far, we have not found any suitable analogs among the hundreds of other high-redshift galaxies in our survey. Considering the relatively small region of the sky we searched to find JADES-GS-z14-0, its discovery profoundly impacts the predicted number of bright galaxies in the early universe, as discussed in a concurrent JADES study by Robertson et al., recently accepted.
It is likely that astronomers will discover many such luminous galaxies, possibly from even earlier times, over the next decade with Webb. We’re thrilled to witness the extraordinary diversity of galaxies that existed at Cosmic Dawn! These spectroscopic observations were part of Guaranteed Time Observations (GTO) program 1287, with the MIRI observations included in GTO program 1180.
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