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REVIEW 4 major objections 5 minor 67 references

Analysis of metal-poor galaxy spectra in the redshift range 0.00574-0.05368

T0 review · 4 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Eleven 'metal-poor' galaxies, re-modelled with shock-and-photoionization modeling, split into AGN (four), starburst (two) and probable-merger (five) classes, with helium and nitrogen — not oxygen — the truly depleted elements.

desk verdict New application of an idiosyncratic modeling code to 11 EMPGs gives interesting classifications, but the headline He/H and N/H values rest on an untested assumption and no uncertainty quantification. read the letter →

arxiv 2412.01304 v1 pith:FNAJHOIW submitted 2024-12-02 astro-ph.GA

Marcella Contini This is my paper · ORCID
classification astro-ph.GA
keywords extrememetal-poorgalaxiesshockwavesphotoionizationactivegalacticnucleistarburstoxygenabundancesnitrogen-to-oxygenratiohelium
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper re-analyses the spectra of eleven 'extreme metal-poor galaxies' (EMPGs) from the Nakajima et al. (2022) sample with the suma code, which treats each spectrum as the combined emission of a shock and a photoionizing flux through the same cloud, with the cloud either accreting toward or ejected from the galaxy's radiation source. The central claim is that the usual pure-starburst, pure-photoionization reading of these galaxies is incomplete: four galaxies are best reproduced by a single AGN model, two by a single starburst model, and five (the four SDSS galaxies plus HSC J1411-0032) fit both types about equally well, which the paper interprets as merger products. The second main finding is chemical: oxygen emerges at most about five times below solar, while helium and nitrogen are depleted by factors up to about 100 and 135, respectively, so the 'extreme metal poverty' of these objects is carried mainly by nitrogen and helium rather than by oxygen. If correct, this means that assuming pure star formation in low-metallicity galaxies can mislabel the power source and that the EMPG label applies to different elements than usually assumed.

What carries the argument

The load-bearing tool is the suma code: a model that pushes both a photoionizing radiation flux and a shock through a plane-parallel cloud divided into up to 300 slabs, solving the ionization, recombination and collisional-ionization balance for twelve elements (H, He, C, N, O, Ne, Mg, Si, S, Ar, Cl, Fe) in each slab and integrating the emitted line ratios to Hβ through the cloud. Its distinguishing feature for this paper is the geometry switch: in the accretion case the ionizing radiation strikes the same cloud edge as the shock front (parameter str=0), while in the ejection case (str=1) it strikes the opposite edge, producing different ionization profiles and therefore different line ratios from the same physical parameters. The governing inputs are the shock velocity $V_s$, the preshock density $n_0$, the preshock magnetic field $B_0 = 10^{-4}$ G, the cloud thickness $D$, the shape of the ionizing radiation (black body for starbursts, power law for AGN), and the element-to-hydrogen abundances; the shock parameters feed the Rankine-Hugoniot jump conditions and the Cox compression law to obtain the downstream density and temperature profile. A candidate model is accepted when the strong lines agree with the observed spectrum within 10-20% and the weak lines within 50%.

What would settle it

Take a high-resolution spectrum of one of the eleven galaxies, for instance SDSS J1044+0353 (N10), and measure the velocity profile of HeI 5876 against the nebular lines. If HeI 5876 shares the velocity width and spatial distribution of Hβ and [OIII] from the modelled clouds, the diffuse-interstellar-medium premise fails and the factor-of-100 helium depletion is not supported; the same observation would also show whether the galaxy has one or two kinematic components, directly testing the merger interpretation for the five dual-classified objects.

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Extended reading notes

Core claim

The paper's claim, stated on its own terms, is that each of the eleven EMPG spectra demands a model with both a shock and a photoionizing flux, and the best-fitting model tells you what the galaxy is. Varying the shock velocity $V_s$, preshock density $n_0$, cloud thickness $D$, the ionizing flux (black body for starbursts, power law for AGN), and the element abundances in both the accretion and ejection geometries, the paper classifies N1, N3, N6 and N9 as AGN-dominated and N5 and N7 as starburst-dominated, while N8, N10, N11, N12 and N13 are equally well matched by an AGN and a starburst model; for these five the paper proposes that the galaxy is the product of merging, so that two radiation sources contribute to the same spectrum. The modelled abundances put $\log(\mathrm{O/H})+12$ mostly in the range 8.0 to 8.9 against a solar value of 8.69, so oxygen is at most about five times below solar and sometimes above it, whereas $\mathrm{He/H}$ is lower than solar by factors up to about 100 and $\mathrm{N/H}$ by factors up to about 135. The conclusion the author draws is that the 'extreme metal poor' classification of these galaxies is justified only if nitrogen and helium count as the poor metals, and that the low $\mathrm{N/O}$ values are the signature of a young bursting starburst in which intermediate-mass stars have not yet released their nitrogen.

Load-bearing premise

The helium abundance is pinned to the HeII 4686 line alone, on the premise that the HeI 5876 line is emitted mostly by diffuse interstellar gas that the models do not include, so the models' poor fit to HeI 5876 is explicitly set aside (Section 2.2.1); if HeI 5876 actually comes from the modelled clouds, the derived helium abundances — and with them the cooling rates, the other element abundances, and the AGN versus starburst classifications — are unsupported.

Editorial extensions

If this is right

  • Four of the eleven galaxies (N1, N3, N6, N9) would harbour AGN that pure-starburst analyses miss, so the EMPG class is not purely star-forming even at low metallicity.
  • The five dual-model galaxies (N8, N10-N13) would be merger products, making composite AGN-plus-starburst systems common at the higher-metallicity end of the sample and tying 'metal-poor' galaxy activity to interaction-driven accretion and ejection.
  • If oxygen is at most about five times below solar while nitrogen is up to about 135 times below solar, oxygen-based strong-line methods systematically underestimate the true metallicity in these systems, and the 'extreme poor metal' label belongs to nitrogen.
  • The low $\mathrm{N/O}$ ratios and their upward turn near $\log(\mathrm{O/H})+12 = 8.7$ fit the bursting star-formation picture in which massive stars have already enriched oxygen while intermediate-mass stars (4-8 $M_\odot$) have not yet released nitrogen, dating these galaxies as very young bursts.
  • He/H values 10 to 100 times below solar, if correct, mean either that helium is genuinely diluted in these clouds or that helium abundances based on HeI recombination lines are contaminated by diffuse interstellar gas and need revision.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The merger interpretation is testable: integral-field spectroscopy of N8 and the four SDSS galaxies should reveal double kinematic components, tidal features, or offset ionised-gas structures in at least some of the five; a single well-ordered velocity field in all five would undercut the merger claim.
  • The diffuse-ISM premise for HeI 5876 predicts a specific observable: that line should be spatially smoother and have a different velocity dispersion than the [OIII] and Hβ lines from the modelled clouds, so narrow-band or IFU imaging can separate the two components and check the premise directly.
  • The factor-10 shift applied to $\mathrm{N/O}$ before comparing with other galaxy samples in the paper's Fig. 11 is an acknowledged uncertainty in the absolute nitrogen scale; redoing the comparison without the shift, or with the shift derived from the collisional and thermal factors, would test how robust the 'nitrogen-poor' conclusion is.
  • Because the sample was selected on oxygen-based metallicity indicators, it may be biased toward nitrogen-poor outliers; a nitrogen-selected or helium-selected survey of low-metallicity galaxies would probe whether extreme nitrogen deficiency is generic to the class or an artefact of the selection.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. The paper applies the shock-plus-photoionization code suma to the optical spectra of eleven low-redshift extreme metal-poor galaxies from Nakajima et al. (2022). For each galaxy it reports a best-fitting combination of shock velocity, preshock density, cloud thickness, ionizing flux, and element abundances, and classifies the object as AGN or starburst, accreting or ejecting. Five objects are claimed to be merger products because both AGN and SB models fit. The paper also derives O/H, He/H, and N/H values, reporting deficiencies relative to solar by factors of up to 5, 100, and 135, respectively, and discusses N/O trends with metallicity and redshift.

Significance. If the derived classifications and abundance ratios were robust, the paper would challenge the purely star-forming interpretation of EMPGs and place strong constraints on helium and nitrogen in extremely metal-poor galaxies. The paper is strongest in its transparency: the appendix tables give complete model line ratios and input parameters for every galaxy, and the line-ratio comparisons cover many diagnostic lines. The N/O-versus-O/H and N/O-versus-redshift compilations across many galaxy types are also a useful reference. However, the central claims currently rest on an unverified assumption about HeI emission and on a manual grid search without uncertainty quantification, so the scientific conclusions are not yet established.

major comments (4)
  1. [Sec. 2.2.1] The decision to set He/H exclusively from HeII 4686/Hbeta while explicitly neglecting HeI 5876/Hbeta is not justified by any modeled or independently constrained contribution from diffuse ISM gas. The paper states that 'the dilemma between an acceptable HeII 4686/Hbeta or an acceptable HeI 5876/Hbeta was resolved by arguing that HeI is a permitted recombination line therefore the contribution from the ISM to the observed line is sensible,' and then adopts reduced He/H and ignores the HeI fit. The mismatch is extreme: for N1 the observed HeI 5876/Hbeta is 0.21 while model mh1.1 gives 0.001, and for N5 the observed value is 0.13 while model mh5.1 gives 0.001 (Table A.3). Because the same section states that He is a strong coolant, lowering He/H by factors of up to 100 changes the downstream thermal structure and therefore every calculated line ratio, abundance, and the AGN/SB classification. The headline He/H, O/H, and N/H values are consequences of this unverified assumption rather than measurements. A concrete test would be to include a separate low-density photoionized ISM component and fit HeI simultaneously, or to demonstrate from an independent observable that the diffuse ISM indeed dominates HeI 5876.
  2. [Sec. 3.2] The merger classification is not supported by the evidence presented. The paper states that 'the galaxies showing a double or even a higher number of radiation sources are generally the product of merging' and then classifies N8, N10, N11, N12, and N13 as merger products because both AGN and SB models fit. With roughly a dozen free parameters (Vs, n0, B0, D, F, U, T*, and five abundances), the existence of two acceptable fits is expected degeneracy, not evidence for two radiation sources. No morphological, kinematic, or stellar-population evidence for merging is provided. The claim that five of eleven galaxies are merging products therefore needs either a quantitative degeneracy analysis (e.g., how many grid models fall within the tolerance and how distinct their parameter vectors are) or independent corroboration, or it should be dropped from the conclusions.
  3. [Sec. 2.1 and Sec. 3.2] The model selection relies on percentage differences that are tiny compared with the stated uncertainties, and no uncertainty budget is given. Figure 1 deliberately omits observed error bars, and the text says fits are acceptable within 10-20% for strong lines and within 50% for weak lines. Yet the classification decisions in Sec. 3.2 use differences such as 1.5% versus 5.6% (N1) or 4.6% versus 28% (N3) to select between models. Since the observed weak-line fluxes carry uncertainties up to 50%, and since no model line-ratio uncertainties are provided, these small differences are not statistically meaningful discriminators. A parameter covariance or grid-density analysis, or at least an explicit statement of how many models are within tolerance for each galaxy, is needed to support the claimed precision of the classifications.
  4. [Table 4] The oxygen metallicities derived here are systematically higher than the Nakajima et al. values by 0.5-1.5 dex (e.g., N3: 7.17 versus 8.0-8.8; N1: 7.35 versus 8.0-8.72), and the paper concludes that 'low oxygen line ratios to Hbeta not always indicate a proportional O/H relative deficiency.' This conclusion depends entirely on the shock-plus-photoionization model and, in particular, on the reduced He/H that follows from the HeI assumption. The O/H values should be shown to be stable under a different treatment of the helium lines before this conclusion is presented as a general statement about EMPGs.
minor comments (5)
  1. [Fig. 1 caption] The word 'Asterix' should be 'asterisks'.
  2. [Sec. 2.2.1] The text contains the typo 'SSDS spectra'; this should be 'SDSS spectra'.
  3. [References] The entry 'Contini, M. 2022 arXiv:2201.06004' (Paper I) lacks journal information; if the work is unpublished, it should be labeled as a preprint, or a published version should be cited.
  4. [Table 4] The column headers '12+log(O/H)0 1' and similar are ambiguous; the accretion/ejection flag (str=0 or str=1) should be stated explicitly in the header.
  5. [Throughout] The text contains several spelling and formatting errors (e.g., 'Y et' instead of 'Yet', 'Kauffmann' with a nonstandard ligature, 'Sancisi ... OOsterloo'); a careful proofreading pass is recommended.

Circularity Check

4 steps flagged · score 6.0 of 10

Core abundance 'results' are the fitted input parameters: He/H and N/H are tuned to reproduce HeII and [NII], then reported as derived abundances, and the Fig. 8 z-trends are the fitting parameters themselves.

  1. fitted input called prediction [Sect. 2.1 (model input) and Sect. 3.3, Fig. 8 'Calculated parameter trends with z']
    "The calculation process is repeated changing the input parameters until the observed data are reproduced by the model results, at maximum within 10-20 percent for the strongest lines and within 50 percent for the weakest ones. ... The calculated parameters were selected by reproducing the data within errors < 20% for the strong lines and <50% for the weak ones."

    The element abundances, shock velocities, densities, geometrical thicknesses, and radiation parameters are free inputs adjusted iteratively until the computed line ratios match the observed ones. The same adjusted values are then reported as 'calculated parameters' and plotted as 'calculated parameter trends with z' in Fig. 8. The trends are therefore not independent predictions or first-principles derivations; they are the fitted inputs themselves, relabeled as outputs.

  2. self definitional [Sect. 2.2.1, 'Helium lines']
    "The parameter which can reduce strongly the HeII line intensity is the He abundance. ... in the following we will adopt reduced or enhanced He/H relative abundances in order to reproduce the HeII4686/Hβ line ratios neglecting the HeI/Hβ fit for both AGN and SB models."

    He/H is an adjustable input, not an independently derived quantity: it is set to the value that makes the model's HeII 4686/Hβ match the observed line. The abstract's claim that 'He/H were calculated lower than solar by factors ≤ 100' reports this chosen input. Because the HeI 5876 fit is explicitly neglected, the reported He/H is the He/H input by construction, and any downstream effects on cooling and on other abundances inherit this circularity.

2 more flagged steps
  1. self definitional [Sect. 2.2.2, 'Nitrogen lines']
    "N/H will directly result by reproducing the observed [NII]/Hβ line ratios."

    N/H is one of the input abundances ('The abundances of the elements ... are input parameters'). The paper tunes N/H until the predicted [NII]6583/Hβ matches the observed value, then presents the resulting value as an abundance finding (N/H lower than solar by factors ≤135). The 'result' is identical to the input chosen for the fit; there is no independent constraint or prediction that could fail.

  2. self citation load bearing [Sect. 3.2, 'Classification of the sample galaxies']
    "The galaxies showing a double or even a higher number of radiation sources are generally the product of merging (Contini 2012, 2013)."

    The identification of five of the eleven sample galaxies as merging products follows directly from this rule, which is supported only by two prior papers by the same author. The criterion is not independently established or externally benchmarked in the present paper, so this part of the classification rests on a self-citation chain rather than on independent evidence or a testable prediction.

full rationale

Most of the paper is a fitting exercise: the suma code's input parameters, including elemental abundances, are varied until the computed optical line ratios match the observed ones, and the resulting best-fit values are then reported as the paper's results. This is not inherently circular when presented as model fitting, but the paper presents the fitted abundances as derived findings ('He/H were calculated lower than solar by factors ≤ 100', 'N/H by factors ≤ 135') and plots the fitted parameters as 'calculated parameter trends with z' in Fig. 8. The He/H and N/H cases are the clearest reductions: each abundance is explicitly selected to force a specific observed line ratio (HeII 4686/Hβ and [NII]/Hβ, respectively), with the HeI 5876 constraint deliberately abandoned. Thus the headline abundance claims are the fitting inputs renamed as outputs, which is the fitted-input-called-prediction / self-definitional pattern. The merger classification is additionally supported only by a same-author citation, making it a load-bearing self-citation, though it is secondary to the abundance claims. I am not counting the assumption that HeI 5876 is dominated by the diffuse ISM as circularity by itself; it is an unverified modeling assumption and hence a correctness risk rather than a definitional reduction. Overall, the central abundance results reduce by construction to the fitted inputs, so a score of 6 is appropriate: partial circularity rather than a fully forced derivation.

Assumptions & free parameters 11 free parameters · 6 assumptions · 0 invented entities

The central claims rest on a large set of manually adjusted input parameters: shock velocity, preshock density, magnetic field, cloud thickness, radiation flux or temperature and ionization parameter, and the abundances of He, N, O, Ne, and S. None of these are derived from independent observations; they are varied until the code reproduces the observed line ratios. The paper also assumes the physical validity of the shock-plus-photoionization geometry, the neglect of HeI for abundance work, and the rule that two equally good fits mean a merger. There are no invented entities, but the abundance and classification results are essentially the free parameters of the fit.

free parameters (11)
  • shock velocity Vs = 100-500 km/s across models
    Adjusted per galaxy to reproduce line ratios; drives post-shock temperature.
  • preshock density n0 = 100-4000 cm^-3
    Chosen to reproduce [OII] and [SII] ratios.
  • magnetic field B0 = 1e-4 G generally, 6e-5 G for two models
    Fixed by hand to set compression; correlated with n0.
  • cloud geometrical thickness D = 1e-4 to 3 pc
    Adjusted to switch matter-bounded versus radiation-bounded models.
  • AGN ionizing flux F = up to 2.2e12 photons cm^-2 s^-1 eV^-1
    Radiation field parameter varied to fit high-ionization lines.
  • SB effective temperature T* and ionization parameter U = T* 3.5e4-1.8e5 K, U up to 0.6
    Black-body SED parameters varied to fit starburst models.
  • He/H abundance = 0.0008 to 0.09 by number
    Fitted to HeII 4686/Hbeta while HeI 5876 is ignored.
  • N/H abundance = 5e-7 to 8e-6 by number
    Fitted to [NII]6583/Hbeta.
  • O/H abundance = 1e-4 to 7e-4 by number
    Fitted to oxygen line ratios; values in Table 4.
  • Ne/H and S/H abundances = Ne/H 0.03e-4 to 1.0e-4; S/H 0.01e-4 to 0.5e-4
    Adjusted to match [NeIII] and [SII] line ratios.
  • N/O scaling factor = 10
    Applied to model N/O ratios in Fig. 11 to align them with other galaxy samples; the factor is not derived from the model.
assumptions (6)
  • standard math Rankine-Hugoniot jump conditions and the Cox (1972) compression equation determine the downstream density profile.
    Invoked in Sect. 2.1 to compute the density profile behind the shock.
  • domain assumption The starburst SED can be approximated by a single black-body and the AGN SED by a power-law with alpha_UV=-1.5 and alpha_X=-0.7.
    Stated in Sect. 2.1 as the adopted radiation field parametrization.
  • domain assumption Charge exchange reactions between O+ and H+ and between N+ and H+ set the [NII]/[OII] line ratio.
    Used in Sect. 2.2 to tie the N/O abundance ratio to the observed line intensities.
  • ad hoc to paper HeI emission is dominated by diffuse ISM, so He/H can be set using HeII 4686 alone while ignoring HeI 5876.
    Introduced in Sect. 2.2.1 to resolve the dilemma between fitting HeI and HeII lines.
  • ad hoc to paper When two or more models fit the spectrum similarly well, the galaxy is a merger product.
    Adopted in Sect. 3.2 to classify galaxies with multiple acceptable models.
  • standard math Atomic coefficients for ionization, recombination, and dielectric recombination are trusted from quantum mechanics.
    The paper states that the accuracy of the calculated coefficients depends on quantum mechanics (Sect. 2.1).

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Pith. "Pith review of Analysis of metal-poor galaxy spectra in the redshift range 0.00574-0.05368." pith.science (2026). https://pith.science/paper/FNAJHOIW

@misc{pith2026241201304,
  author       = {Pith},
  title        = {Pith review of: Analysis of metal-poor galaxy spectra in the redshift range 0.00574-0.05368},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/FNAJHOIW}},
  note         = {Machine review of arXiv:2412.01304}
}
abstract

We present an analysis of the metal-poor galaxy spectra in the redshift range 0.00574$\leq$z$\leq$0.05368 which were reported by Nakajima et al (2022) in their EMPG (extreme metal poor galaxy) sample. The models account for the active galactic nuclei (AGN) and the starburst (SB) galaxies, for accretion and ejection, for the physical parameters and the element abundances. The results are obtained in particular for the two cases, the emitting nebula is ejected outward from the galaxy radiation source (RS) and the emitting nebula is accreted towards the RS. We adopt the code {\sc suma} which allows to choose the direction of the clouds relative to the RS. The modelling results which reproduce a single galaxy spectrum with the highest precision allow to classify this object as an AGN ejecting, an AGN accreting, an SB ejecting or an SB accreting type. When more models are equally valid we suggest that the galaxy is the product of merging. Our results show that among the eleven sample galaxies five are such. We focus on the N/O trends with the oxygen metallicity and with the redshift to identify the nitrogen/oxygen relative formation processes and the process-rates, respectively, for intermediate-mass stars. Our results show that O/H relative abundances calculated for the sample galaxies are lower than solar by a factor $\leq$5. Yet, a few values were found above solar. He/H were calculated lower than solar by factors $\leq$ 100 and N/H by factors $\leq$135.

Figures

Figures reproduced from arXiv: 2412.01304 by the authors.

Figure 1
Figure 1. Calculated (mod) versus observed (obs) line ratios to Hβ. Black symbols refer to accretion, red ones to ejection. Open circles: models (mp) calculated by radiation adapted to an AGN and solar He/H; open triangles: models (mh) calculated by radiation adapted to AGN and by different He/H. Asterix: models (ms) calculated by radiation adapted to starbursts and different He/H. The models are described in the bottom of Ta… view at source ↗
Figure 2
Figure 2. Profiles of the physical parameters throughout the N12 galaxy clouds in the accretion case: the shock front and the edge reached by the AC flux are both on the left. Top diagram: black lines: Te (solid), Ne (dashed); middle diagram: blue: HI (dashed), HII (solid); black : HeI (dashed), HeII (solid); bottom diagram: black lines refer to oxygen ionization stages: [OIV] (dot-dashed), [OIII] (solid), [OII] (dashed); red… view at source ↗
Figure 3
Figure 3. The ejection case. The clouds are divided in two contiguous halves which are displayed by the left and right panels. In the left panel the shock front is on the left and the X-axis scale is logarithmic. In the right panel the right edge is reached by the flux from the AC. The X-axis scale is logarithmic in reverse in order to have the same detailed view of the cloud edges. Symbols as in Fig.2. as for AGN and the He/… view at source ↗
Figures from the paper (9 more)
Figure 4
Figure 4. Figure 4: [OIII]4363/Hβ versus [OIII]5007+4959/Hβ. Yellow filled squares represent the observed values. Other symbols as in [PITH_FULL_IMAGE:figures/full_fig_p008_4.png]
Figure 5
Figure 5. Figure 5: [OIII]4363/Hβ versus [OII]3727+3729/Hβ. Symbols as in [PITH_FULL_IMAGE:figures/full_fig_p008_5.png]
Figure 6
Figure 6. Figure 6: [OII]/Hβ versus [NII]/Hβ. Symbols as in [PITH_FULL_IMAGE:figures/full_fig_p009_6.png]
Figure 7
Figure 7. Figure 7: [OIII]5007+4959/Hβversus HeII4686/Hβ. Symbols as in [PITH_FULL_IMAGE:figures/full_fig_p009_7.png]
Figure 8
Figure 8. Figure 8: Left. Distribution of the calculated physical parameters representing the shock (top panels), of the calculated element relative abundances (middle panels) and of the radiation parameters (bottom diagrams) as function of z for SB (left) and AGN models (right). Yellow c…
Figure 9
Figure 9. Figure 9: Observed [OIII]5007+4959/[OII]4363 vs redshift (yel￾low filled circles). Numbers refer to the shock velocities calcu￾lated by the models in km s−1presented in Appendix A redshift range which is less adapted to extrapolate to higher z. Alternatively, the different trend…
Figure 10
Figure 10. Figure 10: Observed [NII]6583/[OII]3727+3729 vs redshift (yellow filled circles). We have added in [PITH_FULL_IMAGE:figures/full_fig_p013_10.png]
Figure 11
Figure 11. Figure 11: N/O relative abundances as function of 12+log(O/H) calculated in this paper by SB models (blue squares). Open is for ejection, filled for accretion. The calculated N/O ratios are shifted towards higher values by a factor of 10. Symbols for the other galaxy types are e…
Figure 12
Figure 12. Figure 12: N/O relative abundances as function of log(z) calculated in this paper. Symbols as in [PITH_FULL_IMAGE:figures/full_fig_p014_12.png]

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