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The DESIRED temperature-metallicity relations in star-forming regions: probing the Galactic radial and azimuthal metallicity distributions

We analyse a sample of 225 star-forming regions from the DESIRED-E project, each with simultaneous determinations of the electron temperature from ionized nitrogen and oxygen, $T_{\rm e}$([N ii]) and $T_{\rm e}$([O iii]), respectively. We derive new empirical relations connecting the gas-phase metal...

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Main Authors: Martínez Hernández, Isaias Rafael (Author) , Méndez-Delgado, J Eduardo (Author) , Esteban, César (Author) , García-Rojas, Jorge (Author) , Carigi, Leticia (Author) , Rodríguez, Luis F (Author) , Zapata, Luis A (Author) , Rosales-Ortega, F Fabián (Author) , Orte-García, Maialen (Author) , Reyes-Rodríguez, Elena (Author) , Arellano-Córdova, Karla Z (Author) , Kreckel, Kathryn (Author) , Sattler, Natascha (Author) , Morisset, Christophe (Author) , Peimbert, Manuel (Author) , Torres-Peimbert, Silvia (Author) , Peña, Miriam (Author) , Chrobáková, Žofia (Author) , Zari, Eleonora (Author) , Espinoza-Galeas, David A (Author)
Format: Article (Journal)
Language:English
Published: March 2026
In: Monthly notices of the Royal Astronomical Society
Year: 2026, Volume: 546, Issue: 4, Pages: 1-19
ISSN:1365-2966
DOI:10.1093/mnras/stag149
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1093/mnras/stag149
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Author Notes:I. Rafael Martínez-Hernández, J. Eduardo Méndez-Delgado, César Esteban, Jorge García-Rojas, Leticia Carigi, Luis F. Rodríguez, Luis A. Zapata, F. Fabián Rosales-Ortega, Maialen Orte-García, Elena Reyes-Rodríguez, Karla Z. Arellano-Córdova, Kathryn Kreckel, Natascha Sattler, Christophe Morisset, Manuel Peimbert, Silvia Torres-Peimbert, Miriam Peña, Žofia Chrobáková, Eleonora Zari and David A. Espinoza-Galeas
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Summary:We analyse a sample of 225 star-forming regions from the DESIRED-E project, each with simultaneous determinations of the electron temperature from ionized nitrogen and oxygen, $T_{\rm e}$([N ii]) and $T_{\rm e}$([O iii]), respectively. We derive new empirical relations connecting the gas-phase metallicity to the global electron temperature, $T_{\rm e}$(H$^+$), as determined via radio observations. We establish two calibrations: one assuming a homogeneous temperature distribution ($t^2 = 0$, the ‘direct method’), and another accounting for internal temperature fluctuations ($t^2 \,\gt\, 0$). Applying these calibrations to 460 radio observations of Galactic H ii regions spanning Galactocentric distances from ${\sim} 0.1$ to 16 kpc, we determine the radial O/H gradient in the Milky Way under both assumptions. We further compare these nebular gradients to independent metallicity estimates from young O- and B-type stars and Cepheid variables. We find that the $t^2 \,\gt\, 0$ calibration yields a gradient in excellent agreement with stellar-based determinations, whereas the $t^2 = 0$ method underestimates metallicities by up to $\sim$0.3 dex. This discrepancy cannot be reconciled by invoking oxygen depletion on to dust grains or nucleosynthetic processing via the C-N-O cycle in massive stars. We also find that one widely used relation in the literature, assuming $t^2 = 0$, produces an excessively steep gradient - likely due to the use of outdated atomic data and pre-CCD observations. Finally, we explore potential azimuthal variations in the Galactic metallicity distribution driven by the presence of the spiral arms, finding no evidence for variations larger than $\sim$0.1 dex with respect to the general radial gradient.
Item Description:Veröffentlicht: 21. Januar 2026
Gesehen am 13.04.2026
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/stag149

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