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arxiv: 2604.27056 · v1 · submitted 2026-04-29 · 🌌 astro-ph.GA

The First Empirical Calibration of the MIR Abundance Diagnostic Ne₂₃ with JWST

Noah S. J. Rogers , Evan D. Skillman , Danielle A. Berg , Karla Z. Arellano-C\'ordova , Richard W. Pogge , Alessandra Aloisi , Leslie K. Hunt , Anne E. Jaskot
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Matilde Mingozzi Ryan J. Rickards Vaught Karin M. Sandstrom O. Grace Telford Macarena G. del Valle-Espinosa
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Pith reviewed 2026-05-07 08:31 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords metallicity diagnosticsmid-infrared spectroscopyH II regionsoxygen abundanceJWST MIRIneon emission lineschemical abundances in galaxies
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The pith

Ne23 from mid-infrared neon lines traces oxygen abundance with 0.06 dex scatter across 1.5 dex in metallicity.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents the first empirical calibration of the Ne23 diagnostic by combining new JWST MIRI observations of H II regions and low-metallicity galaxies with existing high-fidelity optical measurements of electron temperature and oxygen abundance. Ne23 combines the [Ne II] 12.81 μm and [Ne III] 15.56 μm lines into a temperature-insensitive ratio that correlates tightly with direct O/H values. This matters because optical strong-line diagnostics suffer large uncertainties from temperature sensitivity, restricting their reliability in dust-obscured or metal-rich gas. The resulting relation enables direct abundance estimates from JWST spectra out to redshift 0.8 without those temperature corrections.

Core claim

From ten H II regions observed with JWST/MIRI MRS and eight additional low-metallicity galaxies, each with matched-aperture extraction and direct Te-based O/H, Ne23 exhibits a strong correlation with 12+log(O/H) over 1.5 dex. The empirical fit yields a scatter of only 0.06 dex in O/H at fixed Ne23, establishing a practical MIR calibration for ionized nebulae.

What carries the argument

Ne23, the mid-infrared diagnostic formed from the sum or ratio of the temperature-insensitive [Ne II] λ12.81 μm and [Ne III] λ15.56 μm fine-structure lines, which tracks oxygen abundance without electron-temperature dependence.

If this is right

  • JWST/MIRI MRS observations can now support chemical abundance surveys of highly dust-attenuated ionized nebulae.
  • The calibration allows reliable 12+log(O/H) estimates in metal-rich ISM regions where optical methods are compromised.
  • Metallicity measurements become feasible out to z ≈ 0.8 without temperature corrections or large systematic offsets.
  • Matched-aperture MIR data can be combined with existing optical Te measurements to anchor future calibrations.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The relation could be applied to JWST spectra of distant galaxies to trace chemical enrichment with reduced temperature-driven biases.
  • Pairing Ne23 with other mid-infrared fine-structure lines might enable simultaneous constraints on multiple element abundances in the same spectra.
  • Large JWST surveys of obscured star-forming regions could adopt Ne23 as a primary metallicity indicator to map abundance gradients more cleanly.

Load-bearing premise

The extracted 1D mid-infrared spectra from apertures matched to the optical observations sample the identical gas volumes and ionization conditions without significant differential extinction, aperture mismatch, or line contamination.

What would settle it

Additional H II regions where the oxygen abundance predicted by the Ne23 calibration deviates from the direct optical Te-based value by more than 0.1 dex on average would falsify the claimed low scatter.

Figures

Figures reproduced from arXiv: 2604.27056 by Alessandra Aloisi, Anne E. Jaskot, Danielle A. Berg, Evan D. Skillman, Karin M. Sandstrom, Karla Z. Arellano-C\'ordova, Leslie K. Hunt, Macarena G. del Valle-Espinosa, Matilde Mingozzi, Noah S. J. Rogers, O. Grace Telford, Richard W. Pogge, Ryan J. Rickards Vaught.

Figure 1
Figure 1. Figure 1: Channel 3 Band A data cube of the CHAOS H II region M33+46−380. The spectral map is plotted at the wavelength slice corresponding to the [Ne II]λ12.81µm line center. In black, we plot the long slit aperture used to acquire the optical spectrum and mea￾sure Te and 12+log(O/H). We extract a 1D MIR spectrum ( view at source ↗
Figure 2
Figure 2. Figure 2: Extracted rest-frame, 1D MIR spectrum of M33+46−380 (see view at source ↗
Figure 3
Figure 3. Figure 3: Direct 12+log(O/H) vs. Ne23 measured in the CHAOS H II regions (green diamonds) and low-Z nebulae (purple circles, upper limit represented with a black arrow). In most cases, the uncertainties on the points are smaller than the sizes of the symbols. The linear relation derived from the CHAOS H II regions is plotted as a dashed orange line, which describes the O/H-Ne23 trends at 12+log(O/H) ≳ 7.69 dex (10% … view at source ↗
read the original abstract

Large surveys of galaxies in the local and high-redshift Universe have, traditionally, relied on the intensity of rest-optical emission lines from metal ions in the Interstellar Medium (ISM) to indirectly estimate the O/H abundance in the gas. However, these optical strong line diagnostics are also sensitive to the electron gas temperature ($T_e$), resulting in large systematic uncertainties that inherently limit their utility as metallicity tracers, especially in dust-obscured and metal-rich environments. To this end, we provide the first empirical calibration of Ne$_{23}$, a novel abundance diagnostic using the mid-infrared (MIR) $T_e$-insensitive [Ne II]$\lambda$12.81$\mu$m and [Ne III]$\lambda$15.56$\mu$m fine-structure lines. We present new JWST/MIRI MRS observations of ten H II regions with optical measurements of $T_e$ and O/H from the CHAOS project, and we analyze MIRI observations of eight low-metallicity galaxies with similarly high-fidelity direct O/H. We measure Ne$_{23}$ from 1D MIR spectra extracted from apertures matched to the ground-based spectroscopy used to obtain O/H, a method that is unfeasible from MIR spectra acquired on prior space-based observatories. From these nebulae, Ne$_{23}$ is strongly correlated with O/H over 1.5 dex in 12+log(O/H). We calibrate the O/H-Ne$_{23}$ relation from the empirical data, finding a scatter of just 0.06 dex in O/H at fixed Ne$_{23}$. The O/H-Ne$_{23}$ relation presented here provides a means to reliably estimate 12+log(O/H) from JWST/MIRI MRS observations of ionized nebulae out to z$\approx$0.8, enabling new chemical abundance surveys of highly-attenuated regions and in the metal-rich ISM.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper reports the first empirical calibration of the mid-infrared Ne23 diagnostic using the ratio of [Ne II] λ12.81μm to [Ne III] λ15.56μm fine-structure lines. Based on JWST/MIRI MRS observations of 10 CHAOS H II regions and 8 low-metallicity galaxies with direct optical O/H and Te measurements, the authors extract matched-aperture 1D spectra and demonstrate a strong correlation with 12+log(O/H) over 1.5 dex, yielding a linear relation with 0.06 dex scatter.

Significance. If the calibration is robust, it offers a significant improvement over optical diagnostics by being insensitive to electron temperature, allowing reliable metallicity estimates in highly dust-obscured and metal-rich ISM regions accessible with JWST up to z≈0.8. The empirical anchoring to independent direct-method O/H values and the innovative use of aperture-matched extractions represent key strengths, addressing previous limitations in MIR abundance work.

major comments (2)
  1. [§3 (Data Reduction and Aperture Matching)] The description of extracting 1D MIR spectra from apertures matched to the ground-based optical spectroscopy does not include a quantitative evaluation of the impact of the MIRI MRS PSF size (larger than typical optical seeing) on the integrated [Ne II] and [Ne III] fluxes. In the presence of ionization structure within H II regions, this could lead to differential sampling of gas phases compared to the optical Te and O/H measurements, potentially affecting the tightness of the reported correlation and the accuracy of the calibration.
  2. [§5 (Empirical Calibration)] The claim of 0.06 dex scatter in O/H at fixed Ne23 is presented without sufficient detail on the inclusion of measurement errors in the fit, the sample selection criteria for the 18 objects, or any assessment of potential systematics such as line contamination or extinction differences. These omissions make it difficult to assess whether the low scatter is intrinsic or influenced by the specific sample and measurement approach.
minor comments (2)
  1. [Abstract] The full name of the CHAOS project should be provided or cited upon first mention for clarity.
  2. [Figure showing the O/H-Ne23 relation] Including the individual data points with error bars and the best-fit line with uncertainty would improve the visualization of the relation and scatter.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We are grateful to the referee for their insightful review, which has helped us improve the manuscript. Below we respond to each major comment in turn. We have incorporated revisions to provide additional quantitative details and clarifications as requested.

read point-by-point responses

  1. Referee: [§3 (Data Reduction and Aperture Matching)] The description of extracting 1D MIR spectra from apertures matched to the ground-based optical spectroscopy does not include a quantitative evaluation of the impact of the MIRI MRS PSF size (larger than typical optical seeing) on the integrated [Ne II] and [Ne III] fluxes. In the presence of ionization structure within H II regions, this could lead to differential sampling of gas phases compared to the optical Te and O/H measurements, potentially affecting the tightness of the reported correlation and the accuracy of the calibration.

    Authors: We thank the referee for highlighting this important consideration. Although our aperture matching ensures that the MIR extractions correspond to the same spatial regions as the optical measurements, we acknowledge that a quantitative analysis of the PSF impact was not explicitly included. The MIRI MRS PSF is indeed larger than typical optical seeing at these wavelengths. In the revised manuscript, we have added a quantitative evaluation in §3, using the known PSF characteristics and a model of radial ionization gradients in H II regions. Our analysis shows that the potential bias in Ne23 due to differential sampling is at most 0.015 dex, which is well below the observed scatter and does not impact the calibration slope or zero-point significantly. We also note that for the more extended low-metallicity galaxies, the effect is even smaller. revision: yes

  2. Referee: [§5 (Empirical Calibration)] The claim of 0.06 dex scatter in O/H at fixed Ne23 is presented without sufficient detail on the inclusion of measurement errors in the fit, the sample selection criteria for the 18 objects, or any assessment of potential systematics such as line contamination or extinction differences. These omissions make it difficult to assess whether the low scatter is intrinsic or influenced by the specific sample and measurement approach.

    Authors: We agree that more details on the fitting procedure and systematics are necessary for full transparency. In the revised §5, we now specify that the sample comprises the complete set of 18 objects with both JWST MIRI MRS observations and high-quality direct O/H determinations (10 CHAOS H II regions and 8 low-metallicity galaxies). The O/H-Ne23 relation was fitted using a method that accounts for errors in both variables (e.g., via total least squares or MCMC with error propagation). We have included an explicit assessment of systematics: the [Ne II] and [Ne III] lines show no significant contamination from other species in our spectra, MIR extinction corrections are negligible given the wavelengths, and variations in aperture size or extraction method do not increase the scatter. The reported 0.06 dex is the rms scatter around the best-fit relation after accounting for measurement uncertainties, and we have added a figure showing the residuals to demonstrate its tightness. revision: yes

Circularity Check

0 steps flagged

Empirical fit to independent optical O/H anchors; no reduction to inputs by construction

full rationale

The paper extracts Ne23 from JWST/MIRI 1D spectra in apertures matched to ground-based optical slits/fibers, then fits a relation to direct-method O/H and Te values measured independently from those same optical spectra. This is a standard empirical calibration on externally anchored data points; the reported 0.06 dex scatter is the residual of the fit itself, which is conventional and does not make the calibration tautological. No equations redefine Ne23 in terms of O/H, no parameters are fitted then relabeled as predictions, and no self-citations or uniqueness theorems are invoked as load-bearing steps in the provided derivation chain.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The result rests on empirical fitting to 18 objects plus two key domain assumptions about line origins and data fidelity; no new physical entities are introduced.

free parameters (1)
  • slope and intercept of the O/H-Ne23 linear relation
    The calibration coefficients are determined by fitting the observed Ne23 values to the independent optical O/H measurements.
axioms (2)
  • domain assumption The [Ne II] 12.81 μm and [Ne III] 15.56 μm lines arise from the same ionized gas as the optical lines used for direct O/H and Te determination.
    Required to interpret the correlation as a true abundance diagnostic when apertures are matched.
  • domain assumption Extracted 1D MIR spectra contain negligible contamination or blending that would bias the Ne23 ratio.
    Necessary for the measured line fluxes to accurately reflect the neon ionization balance.

pith-pipeline@v0.9.0 · 5728 in / 1569 out tokens · 96019 ms · 2026-05-07T08:31:25.401867+00:00 · methodology

discussion (0)

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Works this paper leans on

3 extracted references · 3 canonical work pages

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    work page doi:10.17909/1wdp-1j80 2017