First direct electron temperature measurement in [O II] zone in I Zw 18
Year: 2026
Type: article
Abstract: We present new precise measurements of the electron temperatures and oxygen abundances in the southeast knot of I Zw 18, one of the most metal poor blue compact dwarf galaxies known. We used spectroscopic data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). For the first time in I Zw 18, we directly measured the electron temperature in the low-ionization zone using the rarely detected [O II ] λλ 7320,7330 doublet. We also detected the [O III ] λ 4363 and [S III ] λ 6312 auroral lines, which are associated with high- and intermediate-ionization zones, respectively. We derived T e ([O III ]) = 21 200 ± 860 K, T e ([O II ]) = 16 170 ± 950 K, and T e ([S III ]) = 17 290±1750, which highlights a significant temperature difference between the ionization zones. Using these direct temperature measurements, we determined a total oxygen abundance of 12+log(O/H) = 7.066 ± 0.046, log(N/O) = –1.509 ± 0.097, and log(S/O) = –1.558 ± 0.041. Our results extend the calibration of t 2 − t 3 relations to the highest temperatures and provide important anchor points for the temperature structure of extremely metal-poor H II regions, including high-redshift galaxies, for which direct temperature measurements are especially challenging.
Source: Astronomy and Astrophysics
Institutions: National Academy of Sciences of Ukraine, Heidelberg University, Main Astronomical Observatory, Consejo Superior de Investigaciones Científicas, Instituto de Astrofísica de Andalucía, National Observatory, Universidade do Porto, Institute of Astrophysics and Space Sciences, Centro de Astrofísica da Universidade do Porto, Universidad Nacional Autónoma de México
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, Deutsche Forschungsgemeinschaft, Consejo Nacional de Ciencia y Tecnología, Ministerio de Ciencia e Innovación, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Fundação para a Ciência e a Tecnologia, Agencia Estatal de Investigación, Division of Astronomical Sciences, Lawrence Berkeley National Laboratory
Awards: G1011896320, G1079818582, G1143651532, G1286236842, G1358376193, G1813527838, G1863003419, G1998765129, G3083819904, Instituto de Astrofísica e Ciências do Espaço, Instituto de Astrofísica e Ciências do Espaço, G3559887413, G3685081974, G419881185, G42916606, G4501827968, G498139845, G6865020320, G6877102632, Instituto de Astrofísica e Ciências do Espaço, Management and Operations of the National Optical Astronomy Observatory, G7354628648, G8103039852, G8524849061, G8920660035, G939699906, G969889393
OpenAlex ID: W7124246896