JWST observations shed more light on the nature of a distant galaxy
Tomasz Nowakowski
astronomy writer
Stephanie Baum
scientific editor
Andrew Zinin
lead editor
Using the James Webb Space Telescope (JWST), an international team of astronomers has observed a distant faint galaxy designated JADES-GS-z14-1. Results of the observational campaign, July 30 on the arXiv preprint server, provide more insights into the nature and properties of this galaxy.
Launched into space in 2021, JWST is designed to find and investigate the most distant galaxies, providing insights into the early universe. It enables the detection of galaxies within the first 500 million years after the Big Bang.
One of such early galaxies is JADES-GS-z14-1—the faintest spectroscopically confirmed galaxy, at a redshift of about 14.0. The galaxy has an absolute ultraviolet magnitude of -19.0 and is relatively compact as its half-light radius is estimated to not exceed 520 light years. Previous observations of JADES-GS-z14-1 have found that it has a mass of some 100 million solar masses, and a star formation rate (SFR) at a level of about two solar masses per year.
A group of astronomers led by Zihao Wu of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, has employed JWST to conduct deep imaging and spectroscopy of JADES-GS-z14-1. The observations were carried out with JWST's Mid-Infrared Instrument (MIRI), Near-Infrared Camera (NIRCam), and Near-Infrared Spectrograph (NIRSpec), as part of the JWST Advanced Deep Extragalactic Survey (JADES).
"We present extremely deep JWST observations of JADES-GS-z14-1, the faintest spectroscopically confirmed galaxy at redshift z ≈ 14 to date. This object received an unprecedented 70.7-hour MIRI/F770W integration, 16-band NIRCam photometry, and 56 hours of NIRSpec/PRISM spectroscopy as part of the JADES program," the researchers wrote in the paper.
JWST observations only marginally detected JADES-GS-z14-1 in the MIRI/F770W band. Moreover, the study resulted in no significant detection of rest-frame ultraviolet emission lines in deep NIRSpec prism spectroscopy, despite extremely deep observations.
The observations show that JADES-GS-z14-1 has a physical radius of less than 163 light years. The galaxy's stellar mass was found to be about 40 million solar masses, and its star formation rate was confirmed to be approximately two solar masses per year.
By analyzing the star formation history of JADES-GS-z14-1, Wu's team found that its SFR experienced a steep rise in the last 10 million years. During this rise, the galaxy had an average star formation rate of 2.3 per year and formed nearly 70% of its stellar mass.
The astronomers underlined that JADES-GS-z14-1 shows no prominent ultraviolet metal emission lines. This, together with the galaxy's intense star formation, suggests a gas-phase metallicity below 10% solar and potentially a high escape fraction of ionizing photons.
The authors of the paper concluded that their findings could help us better understand the evolution of early galaxies.
"The weakness of metal emission lines suggests that strong nebular lines are not ubiquitous in early galaxies. These results underscore the diversity of early galaxy properties and provide key constraints on the metal enrichment, star formation, and ionizing conditions during the first 300 million years after the Big Bang," the scientists wrote.
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More information: Zihao Wu et al, JADES-GS-z14-1: A Compact, Faint Galaxy at $z\approx14$ with Weak Metal Lines from Extremely Deep JWST MIRI, NIRCam, and NIRSpec Observations, arXiv (2025).
Journal information: arXiv
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