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Extremely Metal-Poor Galaxies in DESI DR1: Connections to Galaxies in the Early Universe

Jipeng Sui, Hu Zou, Dirk Scholte, Amélie Saintonge, Mar Mezcua, Malgorzata Siudek, Wenxiong Li, Wei-Jian Guo, Shufei Liu, Yunao Xiao, Francisco Prada, Siwei Zou, Jessica Nicole Aguilar, Steven Ahlen, Carlos Allende Prieto, Davide Bianchi, David Brooks, Yu-Ling Chang, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Peter Doel, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, ChangHoon Hahn, Dick Joyce, Robert Kehoe, Martin Landriau, Laurent Le Guillou, Yifei Luo, Aaron Meisner, Ramon Miquel, Seshadri Nadathur, Nathalie Palanque-Delabrouille, Will Percival, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Hee-Jong Seo, Joseph Harry Silber, David Sprayberry, Gregory Tarlé, Benjamin Alan Weaver

Abstract

Extremely Metal-Poor Galaxies (XMPGs), defined as having metallicities below 10\% of the solar value, are considered possible local analogs to primordial systems and offer a unique window into early galaxy evolution. This study presents a large-scale search for XMPGs using data from the Dark Energy Spectroscopic Instrument DR1, systematically evaluating their resemblance to high-redshift galaxies. From a parent sample of over 14 million galaxies, we identify 656 (551 new) confirmed XMPGs and 767 (670 new) high-quality candidates via the direct $T_{\mathrm{e}}$ method. Results reveal that XMPGs follow a distinct star-forming main sequence (SFMS) that is elevated and shallower than that of the comparing star-forming galaxies. Notably, at higher stellar masses ($M_{\star} > 10^{7.5} M_{\odot}$), the XMPG SFMS converges with the sequence observed in high-redshift galaxies by James Webb Space Telescope (JWST), indicating that mature XMPGs sustain star formation rates comparable to their primordial counterparts. Furthermore, XMPGs consistently deviate below the local fundamental metallicity relation, mirroring high-redshift galaxy behavior. These findings demonstrate that XMPGs not only exhibit low metallicities but also preserve scaling relations characteristic of the early Universe, confirming their potential value as local laboratories for studying early galaxy formation processes.

Extremely Metal-Poor Galaxies in DESI DR1: Connections to Galaxies in the Early Universe

Abstract

Extremely Metal-Poor Galaxies (XMPGs), defined as having metallicities below 10\% of the solar value, are considered possible local analogs to primordial systems and offer a unique window into early galaxy evolution. This study presents a large-scale search for XMPGs using data from the Dark Energy Spectroscopic Instrument DR1, systematically evaluating their resemblance to high-redshift galaxies. From a parent sample of over 14 million galaxies, we identify 656 (551 new) confirmed XMPGs and 767 (670 new) high-quality candidates via the direct method. Results reveal that XMPGs follow a distinct star-forming main sequence (SFMS) that is elevated and shallower than that of the comparing star-forming galaxies. Notably, at higher stellar masses (), the XMPG SFMS converges with the sequence observed in high-redshift galaxies by James Webb Space Telescope (JWST), indicating that mature XMPGs sustain star formation rates comparable to their primordial counterparts. Furthermore, XMPGs consistently deviate below the local fundamental metallicity relation, mirroring high-redshift galaxy behavior. These findings demonstrate that XMPGs not only exhibit low metallicities but also preserve scaling relations characteristic of the early Universe, confirming their potential value as local laboratories for studying early galaxy formation processes.
Paper Structure (12 sections, 3 equations, 7 figures)

This paper contains 12 sections, 3 equations, 7 figures.

Table of Contents

  1. Introduction
  2. DESI Data and Sample Selection
  3. DESI overview
  4. Star-forming galaxy sample
  5. Metallicity Estimation Method
  6. Our XMPG Sample and Connections to High-$z$ Galaxies
  7. The XMPG sample
  8. The Most Metal-Poor Galaxy
  9. Star-forming main sequence
  10. Fundamental Metallicity Relation
  11. Conclusions
  12. Appendix

Figures (7)

  • Figure 1: Sky coverage and XMPG sample in DESI DR1. The gray background indicates the observed sky areas in DR1, with darker shades corresponding to higher coverage density. Confirmed XMPGs are shown as circles, and XMPG candidates as triangles (see Section \ref{['sec:xmpgs']}), which are color-coded by metallicity. The dashed and dotted lines mark the Galactic and ecliptic planes, respectively.
  • Figure 2: Distributions for our $\mathrm{[O\ III]} \lambda 4363$-detected star-forming galaxies: (a)$N_\mathrm{e}$, (b) $T_{\mathrm{e}} \mathrm{([O\ III])}$, and (c) metallicity, and the corresponding errors in (d-f). Vertical lines indicate medians.
  • Figure 3: Representative examples of low-redshift XMPGs from our sample. The upper row shows three diffuse systems, while the bottom row displays three compact systems. Each panel includes the target name and metallicity (12 + log(O/H)).
  • Figure 4: Parameter distributions for confirmed XMPGs (blue) and XMPG candidates (orange) from DESI DR1: (a) redshift, (b) $r$-band magnitude, (c) $\mathrm{E(B-V)}$, (d) electron density ($N_{\mathrm{e}}$) without assumed values, (e) electron temperature of [O III] ($T_\mathrm{e}$([O III])), (f) log(EW( $\mathrm{[O\ III]} \lambda5007$)), (g) log(SFR), (h) log($M_*$), and (i) log(sSFR).
  • Figure 5: The most metal-poor galaxy in this work (DESI J093402.37+551423.2), a component of the well-known system I Zw 18. Panels (a)-(c) show its Legacy Surveys DR9 data and morphological modelling: (a) color image, (b) best-fit model, and (c) residual map after model subtraction. The red circle marks the 1.5${\arcsec}$ DESI fiber aperture centered on this object; the red cross marks the northwestern component of I ZW 18 (designated as DESIJ093402.01+551427.6). Panel (d) presents the optical spectrum with key emission lines labelled.
  • ...and 2 more figures