J/ApJ/961/173 Extremely metal-poor galaxies at z<1 from DESI (Zou+, 2024) ================================================================================ A large sample of extremely metal-poor galaxies at z<1 identified from the DESI Early Data. Zou Hu, Sui J., Saintonge A., Scholte D., Moustakas J., Siudek M., Dey A., Juneau S., Guo W., Canning R., Aguilar J., Ahlen S., Brooks D., Claybaugh T., Dawson K., de la Macorra A., Doel P., Forero-Romero J.E., Gontcho Gontcho S. A, Honscheid K., Landriau M., Le Guillou L., Manera M., Meisner A., Miquel R., Nie J., Poppett C., Rezaie M., Rossi G., Sanchez E., Schubnell M., Seo H., Tarle G., Zhou Z., Zou S. =2024ApJ...961..173Z ================================================================================ ADC_Keywords: Galaxies, dwarf; Spectra, optical; Abundances; Equivalent widths; Redshifts; Surveys Keywords: Metallicity ; Scaling relations ; Dwarf galaxies ; Redshift surveys 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 Te method based on the detection of the [OIII]{lambda}4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; the remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other properties are provided in the paper. The most XMPGs have an oxygen abundance of ~1/34 Z_{sun}_, a stellar mass of about 1.5x10^7^M_{sun}_, and a star formation rate of 0.22M_{sun}_/yr. 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 ongoing DESI survey. Description: The Dark Energy Spectroscopic Instrument (DESI) is a multi-object spectroscopic system installed at the prime focus of the Mayall 4m telescope at Kitt Peak, in Arizona. It features a 3.2{deg} field of view and provide a continuous wavelength coverage of 3600-9800{AA} for a R~2000 in the blue end to 5000 in the red, which is high enough to resolve the [OII] doublet. The DESI spectroscopic targets include approximately 50 million extragalactic and Galactic objects, mainly selected from the DESI Legacy Imaging Surveys. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 154 95 Properties of our confirmed extremely metal-poor galaxies (XMPGs) table3.dat 154 128 Properties of our candidate XMPGs -------------------------------------------------------------------------------- See also: VI/141 : Nebular [OIII] collision strengths - SSB (Storey+, 2014) VII/292 : DESI Legacy Imaging Surveys DR8 photometric redshifts (Duncan, 2022) V/161 : DESI DR1 redshift catalog (DESI Col.+ 2025) J/ApJS/132/37 : Spectroscopy of Southern warm IR galaxies (Kewley+, 2001) J/ApJ/602/200 : HII regions abund. in blue compact galaxies (Izotov+, 2004) J/ApJS/190/233 : Spectroscopy & abundances of SINGS galaxies (Moustakas+, 2010) J/ApJS/188/32 : Breit-Pauli transition probabilities for SII (Tayal+, 2010) J/ApJ/743/77 : Extremely metal-poor galaxies in SDSS (Morales-Luis+, 2011) J/ApJ/765/140 : Stacked spectra of SDSS star forming galaxies (Andrews+, 2013) J/A+A/568/L8 : VUDS emission line 0.2<~z<~0.9 galaxies (Amorin+, 2014) J/ApJ/819/110 : EMP galaxies in SDSS. II. (Sanchez Almeida+ 2016) J/other/RAA/17.41 : LAMOST metal-poor galaxies sample (Gao+, 2017) J/ApJ/847/38 : Extreme emission line galaxies at z<~0.05 (Yang+, 2017) J/ApJ/863/134 : SDSS low-metallicity blue compact dwarf galaxies (Hsyu+, 2018) J/ApJ/896/77 : The PHLEK survey: oxygen & helium abundances (Hsyu+, 2020) J/ApJS/258/11 : The COSMOS2020 catalog (Weaver+, 2022) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- Seq [1/95] Sequential identifier 4- 7 A4 --- --- [DESI] 9- 27 A19 --- DESI Extremely metal-poor galaxy (XMPG) name (JHHMMSS.ss+DDMMSSs) 29- 45 I17 --- TargetID [234520901058560/39633461119550747] DESI target identifier 47- 55 F9.5 deg RAdeg [30.46/324.3] Right Ascension (J2000) 57- 65 F9.5 deg DEdeg [-27.3/66.7] Declination (J2000) 67- 72 F6.4 --- zspec [0.003/0.9] Spectroscopic redshift 74- 78 F5.2 mag rmag [17.2/25.4] DESI r-band magnitude 80- 83 F4.2 mag EBV [0/0.43] Reddening, E(B-V) 90- 93 F4.2 0.1nm EWOIII [1.6/3.24] Equivalent width of [OIII]5007{AA}, in Angstroms 95- 100 F6.1 cm-3 Ne [100/1064] Electron volume density 102- 107 F6.1 cm-3 e_Ne [0/1156] Uncertainty in Ne 109- 115 F7.1 K Te [17632/23394] Electron temperature for [OIII] 117- 122 F6.1 K e_Te [594/3542] Uncertainty in Te 124- 127 F4.2 [-] logOH [7.16/7.62] Oxygen abundance, 12+log(O/H) 129- 132 F4.2 [-] e_logOH [0.03/0.2] Uncertainty in logOH 134- 138 F5.2 [Msun] logMs [4.36/10.1] Log of stellar mass 140- 143 F4.2 [Msun] e_logMs [0.04/0.5] Uncertainty in logMs 145- 149 F5.2 [Msun/yr] logSFR [-3.8/1.6] Log of star formation rate 151- 154 F4.2 [Msun/yr] e_logSFR [0.1/0.14] Uncertainty in logSFR -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Seq [1/128] Sequential identifier 5- 8 A4 --- --- [DESI] 10- 28 A19 --- DESI Extremely metal-poor galaxy (XMPG) name (JHHMMSS.ss+DDMMSSs) 30- 46 I17 --- TargetID [234514848677892/39633478710462243] DESI target identifier 48- 56 F9.5 deg RAdeg [3.98/339.6] Right Ascension (J2000) 58- 66 F9.5 deg DEdeg [-20.15/68.7] Declination (J2000) 68- 73 F6.4 --- zspec [0.002/0.96] Spectroscopic redshift 75- 79 F5.2 mag rmag [16.39/24.93] DESI r-band magnitude 81- 84 F4.2 mag EBV [0/0.35] Reddening, E(B-V) 91- 94 F4.2 0.1nm EWOIII [1.8/3.84]? Equivalent Width of [OIII]5007{AA}, in Angstroms 96- 101 F6.1 cm-3 Ne [76/1648] Electron volume density 103- 108 F6.1 cm-3 e_Ne [0/1323] Uncertainty in Ne 110- 116 F7.1 K Te [16529/20709] Electron temperature for [OIII] 118- 123 F6.1 K e_Te [480/3499] Uncertainty in Te 125- 128 F4.2 [-] logOH [7.5/7.7] Oxygen abundance, 12+log (O/H) 130- 133 F4.2 [-] e_logOH [0.03/0.3] Uncertainty in OH 135- 138 F4.2 [Msun] logMs [5.77/9.7] Log of stellar mass 140- 143 F4.2 [Msun] e_logMs [0.04/0.76] Uncertainty in logMs 145- 149 F5.2 [Msun/yr] logSFR [-2.4/1.6] Log of Star formation rate 151- 154 F4.2 [Msun/yr] e_logSFR [0.13/0.14] Uncertainty in logSFR -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Apr-2026