New quiescent galaxy discovered with JWST

Using the James Webb Space Telescope (JWST), an international team of astronomers has discovered a new quiescent galaxy. The galaxy, designated JADES-GS+53.15508-27.80178, was found at a high redshift and has a relatively low mass. The finding is reported in a paper published February 27 on the pre-print server arXiv.

Many massive galaxies are quiescent, therefore showing little signs of ongoing star formation even at high redshifts and they are known to be physically compact. To date, only very few spectroscopically confirmed high-redshift (up to the redshift of 5.0) quiescent galaxies have been detected. Finding new galaxies of this type is of high importance for astronomers as these objects could advance our understanding about the early stages of the universe.

Now, a team of astronomers led by Tobias J. Looser of the University of Cambridge, U.K., reports the detection of such a galaxy beyond redshift of 5.0. The discovery was made using JWST’s Near Infrared Camera (NIRCam) as part of the JWST Advanced Deep Extragalactic Survey (JADES).

“Here we report the discovery of a quiescent galaxy at z=7.3, when the universe was only 700 million years old—about 5% of its current age,” the researchers wrote in the paper.

JADES-GS+53.15508-27.80178 (or JADES-GS-z7-01-QU for short) was first identified in 2010 as a Lyman break galaxy. New NIRCam data indicate that it is a quiescent galaxy that experienced a short and intense burst of star formation followed by rapid quenching, about 10 to 20 million years ago.

In particular, the study found that the star formation rate (SFR) of JADES-GS-z7-01-QU increased significantly about 80 million years ago. After this final burst, lasting about 50 million years, the galaxy quenched on a short timescale.

The results show that JADES-GS-z7-01-QU exhibits a complete absence of nebular emission lines, while the Balmer break and Lyman-alpha drop are unambiguously detected. These findings confirm that JADES-GS-z7-01-QU is a post-starburst galaxy that has recently stopped forming stars.

When it comes to the morphology of JADES-GS-z7-01-QU, it appears to be a compact, disk galaxy with a half-light radius of some 650 light years. The images also show a distinct faint source to the East of JADES-GS-z7-01-QU, at a distance of approximately 2,300 light years from the center of the galaxy. The nature of this source is unknown, however the astronomers assume that it may be a clump or a satellite galaxy.

Summing up the results, the authors of the paper noted that their discovery proves how important JWST is for the detection and studies of high-redshift quiescent galaxies.

“We conclude by emphasizing that the discovery and spectroscopic analysis of a quiescent galaxy at redshift z=7.3 by our JADES collaboration ushers the era in which we can constrain theoretical feedback models using direct observations of the primordial universe. However, this is just the starting point for the JWST mission: upcoming and future observations will start the transition from the ‘discovery’ phase to the statistical characterization of the properties of the first quiescent galaxies,” the researchers explained.

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