A Large Sample of Extremely Metal-poor Galaxies at $z<1$ Identified from the DESI Early Data

TL;DR

This study identifies a large sample of 223 extremely metal-poor galaxies at redshift less than 1 from DESI data, providing insights into galaxy formation and evolution in the early universe.

Contribution

It presents the first large-scale sample of XMPGs at z<1 from DESI, including confirmed and candidate galaxies, and analyzes their properties and environments.

Findings

XMPGs are only 0.01% of DESI galaxies.

Most XMPGs have oxygen abundance around 1/34 Z_sun.

XMPGs tend to be in low-density regions and often fall below typical mass-metallicity relations.

Abstract

Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at $z<1$ from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct $T_{\rm e}$ method based on the detection of the [O III]$\lambda$4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other proprieties are provided in the paper. The most XMPG has an oxygen abundance of $\sim 1/34 Z_{\odot}$, stellar mass of about $1.5\times10^7 M_{\odot}$ and star formation rate of 0.22 $M_{\odot}$ yr$^{-1}$. The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass-metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the on-going DESI survey.