An international team of astronomers, utilizing early data from the Dark Energy Spectroscopic Instrument (DESI), has identified a compelling 95 new extremely metal-poor galaxies at a low redshift, as revealed in a paper published on the arXiv pre-print server on December 1.
Extremely metal-poor galaxies (XMPGs), characterized by metallicity below 0.1 of the solar metallicity, offer a unique window into the early stages of galactic evolution. These chemically unevolved galaxies are challenging to observe due to their low masses, making local observations at low redshift particularly valuable for understanding their characteristics and serving as potential analogs for primeval high-redshift galaxies.
Led by Hu Zou from the University of Chinese Academy of Sciences, the team focused on analyzing early DESI data, including the Early Data Release (EDR). Their efforts involved the detection of XMPGs and an exploration of their mass-metallicity relation.
The researchers initially identified 1,623 star-forming galaxies with significant oxygen emission lines. From this pool, they pinpointed 223 extremely metal-poor galaxies at redshifts below 1.0, ultimately confirming 95 as authentic XMPGs, with the remaining 128 categorized as XMPG candidates.
Most notably, the majority of these XMPGs were discovered at a low redshift below 0.3, primarily constituting dwarf galaxies with stellar masses not exceeding 1 billion solar masses. One standout galaxy, DESIJ150535.89+314639.4, exhibited an oxygen abundance at just 1/34th of that of the sun, with a stellar mass around 15 million solar masses and a calculated star-forming rate of 0.22 solar masses per year.
Preliminary imaging examinations of the two most metal-poor galaxies revealed distinct morphologies, hinting at different evolutionary paths and physical origins. However, the astronomers emphasize the need for further studies to confirm this hypothesis.
In summary, the identified extremely metal-poor galaxies from DESI's early data hold the potential to be low-redshift analogs of galaxies at high redshifts, possibly extending up to 6.0 or beyond. These galaxies, with their unique characteristics, present promising opportunities for delving into the universe's early stages of evolution.