JWST Reveals an Extremely Metal-Poor Dwarf Galaxy

Using the James Webb Space Telescope (JWST), astronomers have discovered a new dwarf galaxy, which received designation CAPERS-39810. Further investigation of CAPERS-39810 revealed that it is an extremely metal-poor galaxy. The discovery was detailed in a paper published January 24 on the arXiv pre-print server.

Metal-poor galaxies at high redshift are important probes of early star formation and chemical enrichment. They can also provide insights into the properties of the low-metallicity massive stars that drove the process of reionization in the early universe. One of the tools that is suitable to detect such galaxies is JWST.

Searching for new metal-poor galaxies

Zijian Yu of the Blair Academy in Blairstown, New Jersey and Sijia Cai of the Tsinghua University in Beijing, China, employed JWST’s Near-Infrared Spectrograph (NIRSpec) to search for new high-redshift metal-poor galaxies. Their observations, complemented by data from the Hubble Space Telescope (HST), resulted in the detection of CAPERS-39810.

«In this work, we report the discovery of an extremely metal-poor galaxy at z=3.654 and analyze its spectroscopy and spectral energy distribution (SED) to assess metallicity and physical conditions, placing it among the growing population of chemically primitive systems that JWST has so far uncovered,» the researchers explain.

Small and extremely metal-poor

According to the paper, CAPERS-39810 has a stellar mass of about 104.7 million solar masses and a stellar population age of 270 million years. The star-formation rate of this dwarf galaxy was calculated to be 0.26 solar masses per year.

The collected data indicate that CAPERS-39810 has a metallicity at a level of -1.96 dex. This makes it an extremely metal-poor galaxy (EMPG) and is indicative of its primitive chemical composition, resembling the early stages of galaxy formation in the universe.

The astronomers note that the discovery of CAPERS-39810 further supports the existence of very low-metallicity galaxies at cosmic noon (redshift of about 3.0). Studies of such galaxies could be essential in advancing our knowledge about the processes of chemical enrichment and star formation in young galaxies at the cosmic noon.

More common than previously thought?

The authors of the paper add that the detection of CAPERS-39810 extends the census of EMPGs to the redshift range between local analogs and the numerous metal-poor systems now uncovered at redshifts higher than 6.0.

«Such extremely metal-poor systems may in fact be common throughout the universe. However, current observational constraints make them particularly difficult to identify at intermediate redshifts,» the researchers conclude.

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