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Variations in the 3.3 ${\mu}$m Polycyclic Aromatic Hydrocarbon Feature Across Nearby Galaxies Driven by Metallicity and Radiation Field Spectrum

T0 review · 3 major / 4 minor · reviewed 2026-08-08 · deepseek-v4-flash

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Pith's one-line read The paper shows that the 3.3 µm PAH feature strengthens at low metallicity because PAHs are smaller, not just hotter.

desk verdict Solid, useful methods-plus-survey paper; the metallicity trend is probably real, but the variable-B_PAH continuum subtraction and the trend are entangled enough that the authors should show a fixed-B control before the slopes are taken at face value. read the letter →

arxiv 2608.05286 v1 pith:ATUD6TC6 submitted 2026-08-05 astro-ph.GA

Hannah B. Koziol , Karin Sandstrom , Dalya Baron , Adam K. Leroy , Jérémy Chastenet , Ryan Chown , Daniel A. Dale , Oleg V. Egorov
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Lindsey Hands Mansi Padave Debosmita Pathak Erik Rosolowsky Jessica Sutter Tony D. Weinbeck Thomas G. Williams Alberto Bolatto Médéric Boquien Yixian Cao Enrico Congiu Simon C. O. Glover Hwihyun Kim Ralf S. Klessen Kirsten L. Larson Justus Neumann Elias K. Oakes Hsi-An Pan Ismael Pessa Sumit K. Sarbadhicary Benjamin W. Stadel Jiayi Sun David A. Thilker Leonardo Úbeda
This is my paper · ORCID
classification astro-ph.GA
keywords polycyclicaromatichydrocarbons3.3micronPAHfeaturesizedistributionmetallicityradiationfieldhardnessJWSTNIRCamcontinuumsubtractionbandratios
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

Using JWST NIRCam images of 19 nearby galaxies, this paper argues that the balance between the 3.3 µm PAH band and the 7.7 and 11.3 µm bands is set primarily by gas-phase metallicity, with the radiation field spectrum playing a smaller, separable role. The authors develop a continuum-subtraction procedure for the F335M filter and find that the slope describing PAH-correlated color depends on environment, most strongly on specific star formation rate. After subtracting the continuum they find both the 3.3/7.7 and 3.3/11.3 ratios rise as metallicity falls, across the whole sample. They interpret this as evidence that low-metallicity regions host smaller and more neutral PAH grains, consistent with inhibited growth rather than preferential destruction. If true, PAH band ratios are usable size diagnostics only when both metallicity and radiation field hardness are controlled.

What carries the argument

The central object is the color-color slope $B_{\rm PAH}$, the slope of $F335M/F300M$ versus $F360M/F300M$ in PAH-dominated pixels selected by $F300M/F1130W<0.1$ and $F1130W>3$ MJy/sr. This slope parameterizes how much PAH-correlated emission contaminates the F360M continuum band, and the paper measures it per galaxy and per 1.5 kpc region, finding values from about 1.6 to above 2 that track specific star formation rate and the optical line ratio $[\mathrm{NII}]/\mathrm{H}\alpha$. The slope is inserted into a linear continuum relation derived from earlier F335M subtraction work to make continuum-subtracted F335M maps, which are then ratioed against stellar-subtracted F770W and F1130W maps. The second load-bearing ingredient is a grid of dust models with small, standard, and large PAH size distributions, low, standard, and high ionization, and several radiation field spectra; this grid lets the authors read ratio changes as PAH size changes rather than radiation temperature changes.

What would settle it

Take a low-metallicity galaxy or region and obtain a JWST NIRSpec spectrum across 3.2–3.6 µm alongside F300M/F335M/F360M photometry; if the aliphatic and plateau features do not scale with the 3.3 µm feature according to the paper's $B_{\rm PAH}$ prescription, the continuum-subtracted F335M maps are biased and the metallicity trend could shift. Alternatively, if a radiation field model with fixed PAH sizes can reproduce the full increase in 3.3/11.3 with decreasing metallicity, the size interpretation would fail.

Watch

Extended reading notes

Core claim

The paper's central claim is that the relative strength of the 3.3 µm PAH emission compared to longer-wavelength PAH bands increases toward low gas-phase metallicity, and the dominant cause is a shift to smaller PAH populations rather than a change in the spectrum of the heating radiation. The observed slopes are $y=-1.00\pm0.08\,x+7.07\pm0.69$ for $F335M_{\rm PAH}/F1130W$ (3.3/11.3) and $y=-0.85\pm0.08\,x+5.97\pm0.71$ for $F335M_{\rm PAH}/F770W_{\rm ss}$ (3.3/7.7), with $x=12+\log(\mathrm{O/H})$. Stellar population synthesis models are used to show that metallicity-driven changes in the radiation field spectrum would change the 3.3/11.3 ratio by only about 1.15%, too small to explain the trend. Binning by position in a Baldwin-Phillips-Terlevich (BPT) diagram separates a metallicity sequence in star-forming regions from a radiation-field-hardness sequence in LINER/AGN regions, so both effects operate, but the metallicity-to-size link dominates the 3.3/11.3 ratio.

Load-bearing premise

The method assumes that the F335M/F300M versus F360M/F300M colors of PAH-dominated pixels follow a single straight line in each region whose slope $B_{\rm PAH}$ fully describes the PAH-correlated and stellar emission, so any F360M emission component (aliphatic features, 3.47 µm plateau, PAH continuum) that does not scale linearly with the 3.3 µm PAH emission is correctly removed.

Editorial extensions

If this is right

  • The 3.3/11.3 µm ratio is not a pure PAH-size tracer: at fixed high metallicity it responds to radiation field hardness, while across the full metallicity range the size signal dominates.
  • Continuum-subtracted 3.3 µm maps should use an environment-dependent $B_{\rm PAH}$; using a single fixed slope changes F335M PAH fluxes by up to 21% in high-specific-star-formation regions.
  • Lower-metallicity galaxies such as those reaching $12+\log(\mathrm{O/H})\lesssim8.4$ should show enhanced 3.3/7.7 and 3.3/11.3 ratios, matching the outlying radial profiles of IC 5332, NGC 2835, and NGC 5068.
  • The metallicity trend supports the inhibited-growth scenario for PAH formation, in which the average PAH size decreases where carbon abundance limits growth, rather than destruction of small grains.
  • In AGN/LINER regions, the radiation field remains important: the 7.7/11.3 ratio shifts toward neutral PAHs or older stellar populations, and removing AGN hosts weakens that shift.

Reading between the lines

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

  • A testable implication left implicit is that the weaker F360M PAH-correlated carriers (aliphatic 3.4 µm feature, 3.47 µm plateau, and PAH continuum) are suppressed in active star formation; NIRSpec spectra of high-sSFR PAH-dominated pixels should show a lower 3.4/3.3 ratio than quiescent pixels.
  • If $B_{\rm PAH}$ correlates with specific star formation rate, applying a single global slope to distant galaxies with different sSFR distributions could mimic or hide a metallicity trend; the paper's [NII]/Hα and WISE-based prescriptions give a way to propagate that systematic.
  • The nearly vertical motion in 3.3/11.3 versus 7.7/11.3 space at low metallicity suggests the 3.3/11.3 ratio is a sensitive small-PAH fraction indicator even when 7.7/11.3 changes little; measuring it in galaxies below the metallicity of the current sample could test whether the trend saturates.
  • Because the same $B_{\rm PAH}$ recipe is used to build the maps, any environmental variation in the F360M contamination is partly built into the reported ratios; comparing the annular and galaxy-wide map versions brackets this systematic.
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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

3 major / 4 minor

Summary. This manuscript presents an empirical method to isolate PAH-correlated emission in the JWST NIRCam F335M filter using F300M and F360M continuum subtraction, and applies it to 19 PHANGS galaxies. The authors introduce an environment-dependent slope B_PAH in the F335M/F300M versus F360M/F300M color plane, show that this slope correlates with sSFR and [NII]/Halpha, and use it to construct continuum-subtracted F335M maps. They then measure 3.3/7.7 and 3.3/11.3 micron band ratios as functions of metallicity, galactocentric radius, and optical-line ratios. The central claim is that the 3.3 micron feature strengthens relative to 7.7 and 11.3 micron at low metallicity, implying smaller PAH populations, with radiation field spectrum playing a secondary, separable role.

Significance. The 3.3 micron PAH feature is a promising high-resolution ISM tracer, and this is one of the first systematic, sample-wide studies using the NIRCam medium-band method. The paper is well positioned: it includes 19 galaxies, forward-modeling tests of the slope-recovery bias, an explicit treatment of the environmental dependence of B_PAH, and comparisons to established PAH models (Draine et al. 2021) and stellar population synthesis. If the metallicity trend survives a control for the continuum-subtraction systematics, it will be an important confirmation of inhibited PAH growth at low metallicity. The main limitation is the entanglement between the variable B_PAH used to construct the maps and the environmental trends the maps are used to measure.

major comments (3)
  1. [Section 3.5 / Table 2 / Fig. 7] The F335M_PAH maps used to measure the metallicity trends are produced with a region-dependent B_PAH through Eqs. (3)-(6), and Table 2 shows that B_PAH itself correlates with 12+log(O/H) (rho = -0.28, p << 0.03). The 2-5% difference between the annular and galaxy-wide map versions does not control for this, because the galaxy-wide version still uses per-galaxy B_PAH values that vary with metallicity (Table 1 lists B_PAH ~1.94 for NGC 2835 and ~1.96 for NGC 5068, two of the low-metallicity galaxies that drive the trend in Fig. 7). The paper should re-measure the slopes in Fig. 7 using a fixed, spectroscopically calibrated B_PAH (e.g., the Lai et al. 2020 value or a sample-wide constant) to show that the reported slopes (-1.00 +/- 0.08 and -0.85 +/- 0.08) are not imprinted by the subtraction recipe.
  2. [Section 3.3 / Eqs. (3)-(6)] The method assumes that all PAH-correlated emission in F360M scales linearly with F335M_PAH, so that a single color-color slope B_PAH captures the 3.4 micron aliphatic feature, the 3.47 micron plateau, and the PAH continuum. Section 5.1 explicitly acknowledges that these components are not separated and may vary with environment. The forward-model test in Section 3.3 is built on the same linearity assumption (model F335M from F1130W and F360M from B_PAH), so it cannot validate that assumption. A spectroscopic check (e.g., NIRSpec or PAHFIT-based synthetic photometry like Appendix E, applied to representative pixels spanning the environmental range) is needed to confirm that the F360M PAH-correlated component is proportional to F335M_PAH and to quantify how much an environmental variation in the 3.4 micron or plateau features biases the subtracted maps.
  3. [Section 5.2] The argument that metallicity-dependent radiation field spectral changes are too small to explain the observed trend rests on an FSPS calculation that is not fully specified: the text states that a 0.135 dex change in FUV-optical slope 'corresponds to' a ~1.15% change in 3.3/11.3, but the mapping from the stellar population slope to the PAH band ratio is not shown or accompanied by uncertainties. Because this calculation is load-bearing for the 'primarily PAH size' interpretation, the manuscript should either provide the synthetic-photometry details and the Draine et al. (2021) grid interpolation, or downgrade the claim to 'the stellar-population radiation field change is modest compared to the observed dynamic range'.
minor comments (4)
  1. [Section 6, item 1] There is a duplicate word in 'a new method to to isolate the PAH emission'.
  2. [Acknowledgments] 'Humbolt Research Award' should be 'Humboldt Research Award'.
  3. [Table 3] The table header 'Spearman (rho,p)' followed by two numeric columns is ambiguous; the reader must infer which column corresponds to 3.3/11.3 and which to 3.3/7.7, so the header should explicitly label both ratio columns.
  4. [Appendix B / main text] Equation references in Appendix B ('Equation B1', 'Equation B2') are styled inconsistently with the numbered equations in the main text; unify the formatting.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the metallicity trends are measured from maps, not constructed from the fitted B_PAH slope, and the sign of B_PAH's effect opposes the observed trend.

full rationale

I find no circular derivation. The central result, the decrease of 3.3/11.3 and 3.3/7.7 with increasing metallicity (Figure 7), is an observed correlation between independently constructed maps: F335M_PAH comes from Equations 3-6, F1130W is a direct MIRI measurement, and F770Wss is stellar-subtracted via a separate CIGALE-based procedure. The variable B_PAH slope is an empirical calibration quantity, measured from PAH-dominated pixels (F1130W > 3 MJy/sr, F300M/F1130W < 0.1) and then used to build the F335M_PAH maps; the band ratios are not fit to metallicity through B_PAH. Moreover, algebraically F335M_PAH/F300M = B_PAH * (y_m - A_L20 - B_L20 x_m)/(B_PAH - B_L20), which is a decreasing function of B_PAH for fixed observed colors. Since B_PAH correlates negatively with metallicity (Table 2, rho = -0.28), low-metallicity regions tend to have larger B_PAH, which would suppress F335M_PAH rather than create the observed low-metallicity enhancement. Thus the reported metallicity trend is not manufactured by the variable-B_PAH subtraction; if anything, the slopes in Figure 7 are likely conservative. The paper explicitly compares annular and galaxy-wide B_PAH versions, reporting 2-5% average map differences, and uses this as an error term. The method builds on Lai et al. (2020) and Sandstrom et al. (2023), but B_PAH is refit to the present 19-galaxy sample, and the physical interpretation relies on external Draine et al. (2021) model grids and FSPS stellar-population synthesis, not on a self-citation chain. The paper's own admission that spectroscopy is needed to identify which F360M features drive B_PAH variation is a stated limitation, not evidence of circularity.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The paper introduces no new physical entities such as new particles or new forces. Its free parameters are empirical calibration parameters for continuum subtraction and PAH selection. The main assumptions are standard domain assumptions in ISM astronomy. The most important unmeasured quantity is the exact composition of the F360M PAH-correlated emission, which the paper discusses but cannot directly constrain.

free parameters (5)
  • B_PAH slope (per 1.5 kpc region and per galaxy) = median 1.76, 16th-84th percentile 1.57-1.92 on 1.5 kpc scales
    The slope of F335M/F300M vs F360M/F300M is determined empirically from PAH-bright pixels and then used to construct continuum-subtracted F335M maps. It is not derived from first principles and is allowed to vary with environment.
  • Color cut thresholds (F300M/F1130W < 0.1 and F1130W > 3 MJy/sr) = 0.1 and 3 MJy/sr
    The thresholds for identifying PAH-dominated pixels are hand-chosen (Section 3.3) and directly affect the measured B_PAH and hence the final maps.
  • Stellar contamination coefficient 0.88 for F335M-F300M subtraction in Cycle 2 galaxies = 0.88
    This is fit in Appendix B by maximizing correlation with the three-filter PAH maps; it is not derived from physical first principles.
  • Continuum slope parameters from Lai et al. (2020), A_L20=0.35 and B_L20=0.65 = A_L20 = 0.35, B_L20 = 0.65
    These parameters are taken from prior work as an external calibration of the stellar continuum slope; they are retained as fixed inputs rather than rederived.
  • AGN host list (NGC 1365, NGC 1672, NGC 4303, NGC 7496) = four galaxies
    The paper removes these galaxies for some BPT comparisons; the classification is taken from the literature. This selection affects the interpretation of radiation field trends.
assumptions (5)
  • domain assumption The stellar continuum between F300M and F360M is a linear function in color-color space, as in Lai et al. (2020).
    Equation 1 assumes F335M_cont/F300M = A_L20 + B_L20 (F360M/F300M). This is an empirical stellar population modeling result, not a theorem.
  • domain assumption PAH-correlated emission in F335M and F360M follows a linear scaling in color-color space with a single slope B_PAH.
    Section 3.2, Equation 2, assumes F335M_PAH/F300M = A_S23 + B_PAH (F360M/F300M), i.e., that the ratio of 3.3-micron PAH to 3.4-micron/3.47-micron/PAH-continuum emission is constant within each fit region.
  • domain assumption The F1130W filter trace is a valid PAH-selection tool and its >3 MJy/sr cut picks out PAH-dominated lines of sight rather than hot dust or other emission.
    Section 3.3 uses F1130W>3 MJy/sr as a PAH mask; the authors note dust continuum is present in F1130W at <20% level.
  • domain assumption Draine et al. (2021) PAH emission models correctly predict band ratios for various sizes, charges, and radiation fields, including the 3.3 micron feature cross-section.
    Used in Section 4.2 and Figure 12 to interpret the measured ratios. The paper notes the 3.3 micron feature was not covered by Spitzer and its cross-section is less constrained.
  • domain assumption Optical line ratios such as [NII]/Halpha trace radiation field hardness independently of metallicity.
    Section 5 discusses the correlation between B_PAH and [NII]/Halpha as evidence of radiation field hardness. The paper itself notes that [NII]/Halpha also correlates with metallicity, so this has to be treated carefully.

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Cite this review

Pith. "Pith review of Variations in the 3.3 ${\mu}$m Polycyclic Aromatic Hydrocarbon Feature Across Nearby Galaxies Driven by Metallicity and Radiation Field Spectrum." pith.science (2026). https://pith.science/paper/ATUD6TC6

@misc{pith2026260805286,
  author       = {Pith},
  title        = {Pith review of: Variations in the 3.3 $\mu$m Polycyclic Aromatic Hydrocarbon Feature Across Nearby Galaxies Driven by Metallicity and Radiation Field Spectrum},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/ATUD6TC6}},
  note         = {Machine review of arXiv:2608.05286}
}
abstract

We use JWST NIRCam imaging to investigate the 3.3 ${\mu}$m polycyclic aromatic hydrocarbon (PAH) feature in nearby galaxies. NIRCam observations of the 3.3 ${\mu}$m feature are emerging as a powerful tool for studying the structure of the interstellar medium (ISM) and the conditions of the dust at ~0".1 resolution. These maps require accurate subtraction of the underlying continuum emission. We present an empirical method to isolate the PAH-correlated emission in the F335M filter using the F300M and F360M filters for continuum subtraction. We find that the slope of the F335M/F300M versus F360M/F300M colors for PAH-correlated emission shows a dependence on local ISM properties, with the strongest dependence on specific star formation rate. Weaker emission features captured by these bands appear suppressed relative to the main 3.3 ${\mu}$m feature in regions of active star formation. We find trends in the 3.3/7.7 and 3.3/11.3 ${\mu}$m ratios that suggest changes in PAH size, charge, and heating by a varying radiation field spectrum. We find decreases in both band ratios with increasing metallicity, which we attribute to a shift to smaller PAH populations at low metallicity. Comparison to optical ionized gas line ratios and dust models show that variations in the interstellar radiation field spectrum influence the PAH feature ratios. This analysis supports inhibited growth formation scenarios for the observed PAH band ratio trends with metallicity and emphasizes the importance of considering the local radiation field characteristics and gas-phase metallicity when using these band ratios as PAH property diagnostics.

Figures

Figures reproduced from arXiv: 2608.05286 by the authors.

Figure 1
Figure 1. Example slope (BPAH) measurement for galaxy NGC 2835 shown in red. All pixels in the F335M/F300M and F360M/F300M color space are shown in a 2D histogram where the bin edges are logarithmically spaced in both dimensions. Bins with fewer than 10 pixels are shown as individually scattered points. Only the pixels meeting the criteria to be PAH-dominated, F1130W > 3 MJy sr−1 and F300M/F1130W < 0.1, are used for the binne… view at source ↗
Figure 2
Figure 2. Slope values as a function of sSFR for all 1.5 kpc regions evenly sampled across all galaxies. The slope values were calculated individually in each region, following the same procedure from Section 3. The best fitting line, BPAH = 0.17 ± 0.01 × log10(sSFR/yr−1 ) + 3.5 ± 0.1, was calculated on binned medians and overplotted in black. Average slope and sSFR values from regions inside each galaxy are plotted as variou… view at source ↗
Figure 3
Figure 3. Slope as a function of optical line ratio [NII]/Hα. The grey and filled points represent the same information as [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figures from the paper (21 more)
Figure 4
Figure 4. Figure 4: Left: F335M image of NGC 628. Right: F335MPAH map for NGC 628 made using the slope determined for the full map of NGC 628 on the same color scale. All 19 F335MPAH and continuum maps are shown in Appendix Section C [PITH_FULL_IMAGE:figures/full_fig_p010_4.png]
Figure 5
Figure 5. Figure 5: The ratio of the 3.3 to 11.3 µm (pink) and 7.7 µm (blue) PAH feature fluxes in each galaxy as a function of deprojected galactocentric radius measured in r25 (bottom) and scale radius (top) units. Black vertical dashed lines represent the radial extent of “star formati…
Figure 6
Figure 6. Figure 6 [PITH_FULL_IMAGE:figures/full_fig_p012_6.png]
Figure 7
Figure 7. Figure 7: F335MPAH/F1130W (top) and F335MPAH/F770Wss (bottom), in bins of gas phase metallicity for each galaxy at F1130W resolution. Points show the ratio of the medians calculated from points passing the cuts described in Section 2.3. Data are binned by metallicity with bins 0…
Figure 8
Figure 8. Figure 8: The 3.3/11.3 µm ratio plotted against three optical line tracers, [OIII]/Hβ, [NII]/Hα, and [SII]/Hα. The 2D histogram shows metallicity, with contours representing the 16th, 50th, and 84th percentiles of the counts of data shown in black. All maps are put at 150 pc res…
Figure 9
Figure 9. Figure 9: The 3.3/11.3 µm ratio plotted against the same optical line traces as [PITH_FULL_IMAGE:figures/full_fig_p015_9.png]
Figure 10
Figure 10. Figure 10: BPT (J. A. Baldwin et al. 1981), diagram created using the 150 pc data color coded by three quantities with black contours showing where the 16th, 50th, and 84th percentiles of the data lie. Top panels include data from all galaxies and the bottom panels exclude galax…
Figure 11
Figure 11. Figure 11: 7.7/11.3 plotted against 3.3/11.3 at 150 pc resolution colored by metallicity (top) and [NII]/Hα (bottom) for comparison to D. Baron et al. (2024). We isolate the points that are considered LINERs and AGN (left), LINERs (middle), and star-forming (right). Diamond poin…
Figure 12
Figure 12. Figure 12: The ratio of the 3.3/7.7 µm PAH features versus the ratio of the 3.3/11.3 µm PAH ratios at the F1130W resolution colored by the average sSFR in each bin. Each point is binned radially in the same process as Figures 5 and 6 with bin sizes 0.01 r25. Dust model grids fro…
Figure 13
Figure 13. Figure 13: We plot the values of the band ratios identified by the ‘x’ marks on [PITH_FULL_IMAGE:figures/full_fig_p019_13.png]
Figure 14
Figure 14. Figure 14: Each gray curve shows the score, a combination of the correlation coefficient between the original F335MPAH map made with all three medium band filters and the F335MPAH map made with F335M and F300M only with that coefficient value using Equation B1 with a negative fr…
Figure 15
Figure 15. Figure 15: F335MPAH maps for each galaxy in the PHANGS JWST Cycle 1 Survey using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p026_15.png]
Figure 16
Figure 16. Figure 16: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p027_16.png]
Figure 17
Figure 17. Figure 17: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p028_17.png]
Figure 18
Figure 18. Figure 18: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p029_18.png]
Figure 19
Figure 19. Figure 19: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p030_19.png]
Figure 20
Figure 20. Figure 20: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p031_20.png]
Figure 21
Figure 21. Figure 21: F335MPAH maps for more galaxies using the individually calculated galaxy-wide values shown as open faced points in [PITH_FULL_IMAGE:figures/full_fig_p032_21.png]
Figure 22
Figure 22. Figure 22: The same points as [PITH_FULL_IMAGE:figures/full_fig_p034_22.png]
Figure 23
Figure 23. Figure 23 [PITH_FULL_IMAGE:figures/full_fig_p035_23.png]
Figure 24
Figure 24. Figure 24: 3.3/11.3 plotted against 3.3/7.7 at 150 pc resolution colored by metallicity (top) and [NII]/Hα (bottom) for com￾parison with [PITH_FULL_IMAGE:figures/full_fig_p036_24.png]

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