Two most metal-poor galaxies identified in this work. The left, middle, and right panels respectively display observed images, models, and residuals of objects detected in past DESI imaging surveys. Credit: arXiv (2023). DOI: 10.48550/arxiv.2312.00300
By analyzing the first data from the Dark Energy Spectroscopic Instrument (DESI), an international team of astronomers has identified 95 new extremely metal-poor galaxies with low redshift. The discovery is detailed in an article published December 1 on the preprint server arXiv.
Extremely metal-poor galaxies (XMPG) are those whose metallicity is less than 0.1 of the solar metallicity. Since these galaxies have not evolved chemically, they can provide excellent laboratories for investigating theories of the 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 masses. Therefore, astronomers are interested in observations of local low-redshift XMPGs, because they are seen as possible analogues of young, high-redshift primitive galaxies of this type in terms of mass and metallicity.
Now, a group of astronomers led by Hu Zou at the University of the Chinese Academy of Sciences in Beijing, China, has obtained a large sample of XMPG based on early DESI data.
“This work focuses on the analysis of early DESI data, including Early Data Release (EDR; DESI Collaboration et al. 2023b), detection of XMPGs, and exploration of their mass-metallicity relationship,” they wrote the researchers in the article.
In total, the team first selected 1,623 star-forming galaxies with significant detection of oxygen emission lines. From this sample, they identified 223 extremely metal-poor galaxies with redshifts less than 1.0. Ultimately, they confirmed that 95 of them were true XMPGs, while all 128 galaxies remained XMPG candidates.
Most of the XMPGs reported in the study were found with low redshift below 0.3 and were found to be dwarf galaxies, with stellar masses not exceeding 1 billion solar masses. The most metal-poor galaxy in the sample, designated DESIJ150535.89+314639.4, has an oxygen abundance at a level only 1/34 that of the sun, has a stellar mass of about 15 million solar masses and its star-formation rate was calculated to be 0.22 solar masses per year.
The astronomers noted that preliminary imaging examination of the two most metal-poor galaxies discovered from their sample revealed two different morphologies. This suggests different evolution and physical origins; however, additional studies are needed to confirm this hypothesis.
Summarizing the results, the paper’s authors pointed out that the extremely metal-poor galaxies detected by them are possibly low-redshift analogues of high-redshift galaxies reaching 6.0 or even beyond. They could therefore constitute excellent objects for exploring the universe in its early stages of evolution.
More information:
Hu Zou et al, A large sample of extremely metal-poor galaxies at z < 1 identified from early DESI data, arXiv (2023). DOI: 10.48550/arxiv.2312.00300
Journal information:
arXiv
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