Analyzing the first data from the Dark Energy Spectroscopic Instrument (DESI), an international team of astronomers discovered 95 new galaxies with extremely low metal content at low redshift. The finding is detailed in a paper published on the preprint server on December 1 arXiv.

Extremely metal-poor galaxies (XMPGs) are galaxies whose metallicity is less than 0.1 that of the Sun. Given that these galaxies are chemically immature, they can serve as excellent laboratories for investigating theories of chemical evolution of galaxies and studying physical processes in the early stages of their evolution.

Although XMPGs are thought to be quite common at high redshift, they are difficult to observe due to their low mass. Astronomers are therefore interested in observations of low-redshift local XMPGs because they are perceived as possible mass and metallicity analogues of such primitive high-redshift young galaxies.

Now, a team of astronomers led by Hu Zou of the Chinese Academy of Sciences University in Beijing, China, has obtained a large sample of XMPG based on early DESI data.

“This work, Early Data Release (EDR; DESI Collaboration et al. 2023b), focuses on the analysis of early DESI data, including the detection of XMPGs and the investigation of their mass-metallicity relationships,” the researchers wrote in the paper.

In total, the team first selected 1,623 star-forming galaxies where significant oxygen emission lines were detected. From this sample, they identified 223 extremely metal-poor galaxies with redshifts below 1.0. In the end, they confirmed that 95 of them are true XMPGs, while 128 galaxies remain XMPG candidates.

Most of the XMPGs reported in the study were found at low redshifts below 0.3 and turned out to be dwarf galaxies with stellar masses less than 1 billion solar masses. The metal-rich galaxy in the sample, called DESIJ150535.89+314639.4, has an oxygen excess of only 1/34 of that of the Sun, a stellar mass of about 15 million solar masses, and a star formation rate of 0.22. Annual solar mass.

Astronomers stated that a preliminary examination of the images of the two most metal-rich galaxies found in their samples revealed two different morphologies. This suggests a different evolution and physical origin; however, further research is needed to confirm this hypothesis.

Summarizing the results, the authors of the paper emphasized that the extremely metal-poor galaxies they discovered may be low-redshift counterparts of high-redshift galaxies reaching 6.0 or more. Therefore, they may be excellent objects for studying the universe in the early stages of evolution.