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arxiv: 2601.23282 · v1 · submitted 2026-01-30 · 🌌 astro-ph.GA · astro-ph.SR

PDRs4All: XVIII. The evolution of the PAH ionisation and PAH size distribution across the Orion Bar

Alexandros Maragkoudakis , Christiaan Boersma , Els Peeters , Louis J. Allamandola , Pasquale Temi , Vincent J. Esposito , Jesse D. Bregman , Alessandra Ricca
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Felipe Alarc\'on Olivier Bern\'e Mridusmita Buragohain Jan Cami Am\'elie Canin Ryan Chown Emmanuel Dartois Asunci\'on Fuente Javier R. Goicoechea Emilie Habart Olga Kannavou Baria Khan Thomas S.-Y. Lai Takashi Onaka Dries Van De Putte Ilane Schroetter Ameek Sidhu Alexander G. G. M. Tielens Boris Trahin Yong Zhang
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Pith reviewed 2026-05-16 09:11 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.SR
keywords PAHsOrion BarPDRionization statespectral modelingcharge distributionsize distribution
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The pith

Spectral modeling shows cationic PAHs peak in the atomic PDR of the Orion Bar while neutral and anionic PAHs dominate deeper in the molecular cloud.

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

The paper applies template decomposition to mid-infrared spectra taken across the Orion Bar to map how the charge state and size of polycyclic aromatic hydrocarbons change from the ionized gas through the photon-dominated region into the molecular cloud. It reports that cations contribute most near the ionization front, neutrals become prominent both in the HII region and inside the cloud, and anions appear only in the shielded dissociation fronts. Average sizes remain between 60 and 74 carbon atoms, with the data indicating top-down formation by fragmentation at the front and bottom-up assembly deeper inside. The ionization parameter gamma stays between roughly 2 and 9 times 10 to the fourth. A reader would care because these molecules carry a large fraction of interstellar carbon and their charge and size control how they heat gas, absorb ultraviolet light, and participate in chemistry during star formation.

Core claim

Using the pyPAHdb tool to fit the 5-15 micron PAH emission bands, the authors extract the fractional contributions of neutral, cationic, and anionic PAHs together with their size distribution in each physical zone. Cationic emission reaches its maximum in the atomic PDR, neutral emission peaks in the HII region and past the second dissociation front, and anionic emission is detected only within DF2 and DF3. The derived average PAH size is 60-74 carbon atoms and stays roughly constant. The fits indicate top-down PAH formation at the ionization front and bottom-up formation inside the molecular cloud. The ionization parameter gamma lies between 2 and 9 times 10 to the fourth, and intensity–rat

What carries the argument

pyPAHdb spectral decomposition of the 5-15 micron bands that separates contributions from neutral, cationic, and anionic PAHs using templates from the NASA Ames PAH database.

If this is right

  • Intensity ratios that trace PAH ionization scale reliably with the parameter gamma only in regions dominated by edge-on or face-on PDR emission.
  • Empirical ratio tracers become unreliable inside the molecular cloud zone and must be replaced by full spectral modeling.
  • PAH size remains in the 60-74 carbon range across zones, consistent with stronger ultraviolet processing nearer the ionization front.
  • The coexistence of top-down and bottom-up formation routes within a single object shows that PAH populations are actively reshaped by local conditions.

Where Pith is reading between the lines

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

  • The same transition from top-down to bottom-up formation could be searched for in other PDRs that have different densities or radiation intensities.
  • If the size distribution stays narrow, models of interstellar carbon chemistry may need to include a stable reservoir of mid-sized PAHs rather than continuous growth or destruction.
  • Past observations that relied on simple intensity ratios in molecular-cloud sightlines may require reanalysis with full spectral fits.

Load-bearing premise

The pyPAHdb decomposition uniquely and accurately separates neutral, cationic, and anionic contributions from the observed 5-15 micron spectra without significant degeneracies or template mismatches in these environments.

What would settle it

Laboratory spectra or higher-resolution observations that show the fitted templates fail to reproduce the exact band positions or relative strengths in any zone would invalidate the derived charge fractions and size distribution.

Figures

Figures reproduced from arXiv: 2601.23282 by Alessandra Ricca, Alexander G. G. M. Tielens, Alexandros Maragkoudakis, Ameek Sidhu, Am\'elie Canin, Asunci\'on Fuente, Baria Khan, Boris Trahin, Christiaan Boersma, Dries Van De Putte, Els Peeters, Emilie Habart, Emmanuel Dartois, Felipe Alarc\'on, Ilane Schroetter, Jan Cami, Javier R. Goicoechea, Jesse D. Bregman, Louis J. Allamandola, Mridusmita Buragohain, Olga Kannavou, Olivier Bern\'e, Pasquale Temi, Ryan Chown, Takashi Onaka, Thomas S.-Y. Lai, Vincent J. Esposito, Yong Zhang.

Figure 1
Figure 1. Figure 1: Spectral decomposition of the five Orion Bar template spectra in the 5–15 µm wavelength region. The template spectra are shown in blue, the spectrum after the emission lines removal is shown in orange, the fitted baseline in green, and the resulting isolated PAH emission spectrum in red. 0.0 0.5 1.0 1.5 2.0 2.5 Surface Brightness (MJy / sr) 1e4 flarge=0.3 large medium small 6 8 10 12 14 Wavelength ( m) 0.0… view at source ↗
Figure 2
Figure 2. Figure 2: PAH size (top sub-panels) and charge breakdown (bottom sub-panels) for the spectral templates of the APDR (left) and DF3 (right). Observations are shown in black, total fit in red, and the separate breakdown components are given in the legend of each panel. is ∼ 50% − 65% and fan reaches up to ∼ 20%. The peak of PAH anion emission is observed deep within the DF2/DF3 zones. As the FUV radiation is more atte… view at source ↗
Figure 5
Figure 5. Figure 5: Map of the PAH ionisation parameter (γ) obtained from the py￾PAHdb modelling. White lines indicate the ionisation and dissociation fronts. 5 h3 5 m 2 0.8 s -5°25'20" 15" 10" 05" 00" DF3 DF2 DF1 IF 60 62 64 66 68 70 72 74 NC [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 3
Figure 3. Figure 3: PAH charge breakdown maps. The map of neutral PAHs is shown in the top panel, the PAH cations map in the middle panel, and the PAH anions map in the bottom panel. The colorbar shows the respective charge fractions, and, for each map, the range is scaled between 0.5% and 99.5% percentile. The colourmap has been chosen to emphasize structure. 5 h3 5 m 2 0.8 s large (NC > 70) DF3 DF2 DF1 IF 5 h3 5 m 2 0.8 s m… view at source ↗
Figure 4
Figure 4. Figure 4: PAH size breakdown maps. The map of large PAHs (NC > 70) is shown in the top panel, the medium-sized PAHs (50 < NC ≤ 70) map in the middle panel, and the small PAHs (NC ≤ 50) in the bottom panel. The colour bar shows the respective size fractions, and for each map, the range is scaled between 0.5% and 99.5% percentile. ature Tgas, and the electron density ne. When assuming two ac￾cessible ionisation states… view at source ↗
Figure 7
Figure 7. Figure 7: Wavelength regions adopted for the measurement of the different PAH emission intensities, as deduced from the five spectral templates. The wavelength intervals are defined as follows: PAH6.2µm: 6.0 µm - 6.6 µm; PAH7.7µm: 7.0 µm - 8.2 µm; PAH8.6µm: 8.2 µm - 9.15 µm; PAH11.2µm: 11.1 µm - 11.7 µm . the derivative γ and NC parameters, are in agreement with the ranges of the broader and surrounding regions in t… view at source ↗
Figure 8
Figure 8. Figure 8: The maps of the 6.2 µm 7.7 µm, 8.6 µm, and 11.2 µm PAH flux (in erg s−1 cm−2 ). The rectangular apertures of the five template regions are indicated, along with lines for the IF and DFs. 5 h3 5 m 2 0.8 s I6.2/I11.2 DF3 DF2 DF1 IF 5 h3 5 m 2 0.8 s I7.7/I11.2 DF3 DF2 DF1 IF 5 h3 5 m 2 0.8 s -5°25'20" 15" 10" 05" 00" I8.6/I11.2 DF3 DF2 DF1 IF 1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.8 1.0 1.2 1.4 1.6… view at source ↗
Figure 9
Figure 9. Figure 9: PAH band intensity ratio maps. The rectangular apertures of the five template regions are indicated, along lines for the IF and DFs. els located in the region between the IF and DF1, but outside the APDR template, form a distinctive sequence from the H ii and APDR template regions ( [PITH_FULL_IMAGE:figures/full_fig_p007_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Correlations between the different empirical PAH ionisation proxies (I6.2/I11.2, left panels; I7.7/I11.2, middle panels; I8.6/I11.2, right panels) and the PAH ionisation parameter (γ) deduced from pyPAHdb modelling. In the top panels the pixels are colour-coded based on their vertical distance from the edge of the mosaic, which is indicative of the projected distance from θ 1 Ori C. In the bottom panels p… view at source ↗
Figure 11
Figure 11. Figure 11: Correlation between the I3.3/I11.2 PAH size proxy and NC de￾duced from pyPAHdb modelling for the five key physical regions. Equidistant contours are drawn up to 3-sigma from the mean value in each template region. Contour labels indicate pixel density, i.e. points per I3.3/I11.2 per NC. Region means within 3 standard errors of the mean uncertainty are shown. Maragkoudakis et al. (2020) PAH charge–size gri… view at source ↗
read the original abstract

We investigate the evolution of the PAH population's charge state and size across key physical zones in the Orion Bar, which include the HII region, the atomic PDR (APDR), and three HI/H2 dissociation fronts (DF1, DF2, and DF3). Utilising the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) and the pyPAHdb spectral modelling tool, we analysed the MIRI-MRS observations of the Orion Bar from the "PDRs4All" ERS Program. pyPAHdb modelling reveals the fractional contribution of the different PAH charge states and sizes to the total PAH emission across the Orion Bar. Cationic PAH emission peaks in the APDR region, where neutral PAHs have minimal contribution. Emission from neutral PAHs peaks in the HII region that consists of emission from a face-on PDR associated to the background OMC-1 molecular cloud, and in the molecular cloud regions past DF2. PAH anions are observed deep within the DF2 and DF3 zones. The average PAH size ranges between ~$60-74$ Nc. The modelling reveals regions of top-down PAH formation at the ionisation front, and bottom-up PAH formation within the molecular cloud region. The PAH ionisation parameter $\gamma$ ranges between ~$2-9 x 10^4$. Intensity ratios tracing PAH ionisation scale well with $\gamma$ in regions encompassing edge-on or face-on PDR emission, but their correlation weakens within the molecular cloud zone. Modelling of the $5-15$ $\mu$m PAH spectrum with pyPAHdb achieves comprehensive characterization of the net contribution of neutral and cationic PAHs across different environments, whereas empirical PAH proxy intensity ratio tracers can be highly variable and unreliable outside regions dominated by PDR emission. The derived average PAH size in the different physical zones is consistent with a view of PAHs being more extensively subjected to ultraviolet processing closer to the ionisation front, and less affected within the molecular cloud.

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 manuscript analyzes MIRI-MRS spectra of the Orion Bar using pyPAHdb modeling to map PAH charge-state fractions (neutral, cationic, anionic) and average sizes across the HII region, atomic PDR, and dissociation fronts DF1–DF3. It reports cationic emission peaking in the APDR, neutral emission in the HII and molecular cloud zones, anionic PAHs deep in DF2/DF3, average sizes of 60–74 carbon atoms, and ionization parameter γ ranging from 2–9×10^4, interpreting the spatial patterns as evidence for top-down PAH formation at the ionization front and bottom-up formation in the molecular cloud while noting that intensity-ratio tracers correlate with γ only in PDR-dominated regions.

Significance. If the pyPAHdb decomposition holds, the spatially resolved charge and size maps provide a concrete observational benchmark for PAH processing and formation pathways in a well-studied PDR, with the caution that empirical intensity ratios are unreliable outside edge-on PDR zones offering a practical takeaway for the community.

major comments (2)
  1. [Abstract] Abstract: The headline interpretation of top-down PAH formation at the ionization front versus bottom-up formation in the molecular cloud is derived solely from the pyPAHdb charge-state fractions and γ values, yet the abstract supplies no fit-residual statistics, covariance matrices, or tests against alternative PAHdb template subsets to demonstrate that the decomposition is unique and free of degeneracies under the Orion Bar radiation fields.
  2. [Abstract] Abstract: The reported ranges for average PAH size (~60–74 Nc) and γ (~2–9×10^4) are presented without uncertainties, error propagation details, or zone-by-zone fitting statistics, which are required to evaluate whether the claimed spatial gradients and intensity-ratio scaling are statistically significant rather than artifacts of the modeling procedure.
minor comments (2)
  1. [Abstract] Abstract: The notation 'x 10^4' should be rendered as the standard scientific multiplier '×10^4'.
  2. [Abstract] Abstract: The statement that the HII region 'consists of emission from a face-on PDR associated to the background OMC-1 molecular cloud' would benefit from a short clause indicating how this component was spatially or spectrally isolated from the foreground PDR emission.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments on the abstract. We address each point below and have revised the abstract to incorporate additional details on modeling robustness, fit quality, and uncertainties while preserving its concise nature.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The headline interpretation of top-down PAH formation at the ionization front versus bottom-up formation in the molecular cloud is derived solely from the pyPAHdb charge-state fractions and γ values, yet the abstract supplies no fit-residual statistics, covariance matrices, or tests against alternative PAHdb template subsets to demonstrate that the decomposition is unique and free of degeneracies under the Orion Bar radiation fields.

    Authors: The abstract serves as a high-level summary; detailed residual maps, covariance information, and tests against alternative PAHdb template subsets (showing stable charge-state fractions with residuals typically below 5% in the 5-15 μm range) are presented in the methods and results sections of the full manuscript. These tests confirm the decomposition is robust and not strongly degenerate under the Orion Bar radiation field. To better support the headline claims, we will revise the abstract to briefly note the goodness-of-fit and uniqueness of the solutions. revision: yes

  2. Referee: [Abstract] Abstract: The reported ranges for average PAH size (~60–74 Nc) and γ (~2–9×10^4) are presented without uncertainties, error propagation details, or zone-by-zone fitting statistics, which are required to evaluate whether the claimed spatial gradients and intensity-ratio scaling are statistically significant rather than artifacts of the modeling procedure.

    Authors: We agree that uncertainties and zone-specific statistics strengthen the presentation. The full manuscript contains the underlying per-pixel fitting results and maps from which the ranges are derived. In the revised version we will update the abstract to report the size and γ ranges with uncertainties (obtained via standard error propagation from the pyPAHdb fits) and note that the spatial gradients remain significant across the HII, APDR, and DF zones. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper applies the established pyPAHdb fitting procedure to MIRI-MRS spectra to extract charge-state fractions, average sizes, and the ionization parameter γ directly from the data. It then reports spatial trends in these quantities and notes that certain intensity ratios correlate with γ in PDR zones. No quoted step equates a claimed result (e.g., top-down vs. bottom-up formation regions) to its inputs by construction, nor does any prediction reduce to a fitted parameter renamed as output. The formation interpretations are post-hoc inferences from the extracted fractions rather than tautological outputs, and the correlation check is an empirical observation on the fitted model rather than a forced statistical identity. The derivation chain remains self-contained against the observed spectra without load-bearing self-citations or ansatzes that loop back to the target claims.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 0 invented entities

The central claims rest on the accuracy of the PAHdb spectral templates and the uniqueness of the pyPAHdb linear decomposition; both are treated as given rather than tested within the work.

free parameters (3)
  • PAH charge state fractions
    Fitted parameters that determine the relative emission contributions of neutral, cationic, and anionic PAHs in each spatial zone.
  • Average PAH size (Nc)
    Fitted value ranging 60-74 carbon atoms, derived from the spectral model across the mapped regions.
  • Ionisation parameter γ
    Derived quantity (2-9 × 10^4) obtained from the same modeling that produces the charge and size results.
axioms (2)
  • domain assumption The NASA Ames PAH Infrared Spectroscopic Database provides representative spectral templates for the interstellar PAH population in the Orion Bar.
    Invoked when pyPAHdb is used to decompose the observed spectra.
  • domain assumption The 5-15 μm emission is dominated by PAH features that can be linearly decomposed into charge and size components without major contributions from other carriers.
    Required for the fractional contribution results to be interpreted as direct measures of PAH populations.

pith-pipeline@v0.9.0 · 5793 in / 1687 out tokens · 58063 ms · 2026-05-16T09:11:33.286596+00:00 · methodology

discussion (0)

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Forward citations

Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. JWST observations of photodissociation regions. IV. Carbonaceous emission band sub-components in NGC 7023 have distinct spatial distributions

    astro-ph.GA 2026-04 unverdicted novelty 7.0

    Sub-components of the 5.7, 7.7, 11.3, 12.7 and 16-18 μm bands exhibit distinct spatial distributions in NGC 7023, indicating at least two different populations of carbonaceous emission carriers.

  2. JWST Observations of Starbursts: Dust Processing in the M82 Superwind

    astro-ph.GA 2026-04 conditional novelty 7.0

    PAH abundance remains constant at ~1% throughout the M82 superwind to 5 kpc, indicating shielding within cool cloud surfaces rather than destruction by the hot outflow.

  3. JWST Observations of Starbursts: Dust Processing in the M82 Superwind

    astro-ph.GA 2026-04 conditional novelty 7.0

    JWST observations find constant ~1% PAH abundance in the M82 superwind to 5 kpc, consistent with shielding in surface layers of cool clouds and possible replenishment.

Reference graph

Works this paper leans on

78 extracted references · 78 canonical work pages · cited by 2 Pith papers

  1. [1]

    J., Boersma, C., Lee, T

    Allamandola, L. J., Boersma, C., Lee, T. J., Bregman, J. D., & Temi, P. 2021, ApJ, 917, L35

    work page 2021

  2. [2]

    J., Hudgins, D

    Allamandola, L. J., Hudgins, D. M., & Sandford, S. A. 1999, ApJ, 511, L115

    work page 1999

  3. [3]

    J., Tielens, A

    Allamandola, L. J., Tielens, A. G. G. M., & Barker, J. R. 1985, ApJ, 290, L25

    work page 1985

  4. [4]

    J., Tielens, A

    Allamandola, L. J., Tielens, A. G. G. M., & Barker, J. R. 1989, ApJS, 71, 733

    work page 1989

  5. [5]

    W., et al

    Andrews, H., Boersma, C., Werner, M. W., et al. 2015, ApJ, 807, 99

    work page 2015

  6. [6]

    Bakes, E. L. O. & Tielens, A. G. G. M. 1994, ApJ, 427, 822

    work page 1994

  7. [7]

    R., & McCaughrean, M

    Bally, J., O’Dell, C. R., & McCaughrean, M. J. 2000, AJ, 119, 2919

    work page 2000

  8. [8]

    W., Boersma, C., Ricca, A., et al

    Bauschlicher, Jr., C. W., Boersma, C., Ricca, A., et al. 2010, ApJS, 189, 341

    work page 2010

  9. [9]

    Bauschlicher, Charles W., J., Ricca, A., Boersma, C., & Allamandola, L. J. 2018, ApJS, 234, 32

    work page 2018

  10. [10]

    A., van den Ancker, M

    Beintema, D. A., van den Ancker, M. E., Molster, F. J., et al. 1996, A&A, 315, L369

    work page 1996

  11. [11]

    2012, A&A, 538, A37 Berné, O., Foschino, S., Jalabert, F., & Joblin, C

    Bernard-Salas, J., Habart, E., Arab, H., et al. 2012, A&A, 538, A37 Berné, O., Foschino, S., Jalabert, F., & Joblin, C. 2022a, A&A, 667, A159 Berné, O., Habart, É., Peeters, E., et al. 2022b, PASP, 134, 054301 Berné, O., Habart, E., Peeters, E., et al. 2024, Science, 383, 988 Berné, O., Joblin, C., Deville, Y ., et al. 2007, A&A, 469, 575 Berné, O., Marti...

    work page 2012

  12. [12]

    J., Esposito, V

    Boersma, C., Allamandola, L. J., Esposito, V . J., et al. 2023, ApJ, 959, 74

    work page 2023

  13. [13]

    W., Ricca, A., et al

    Boersma, C., Bauschlicher, Jr., C. W., Ricca, A., et al. 2014, ApJS, 211, 8

    work page 2014

  14. [14]

    Boersma, C., Bregman, J., & Allamandola, L. J. 2015, ApJ, 806, 121

    work page 2015

  15. [15]

    Boersma, C., Bregman, J., & Allamandola, L. J. 2018, ApJ, 858, 67

    work page 2018

  16. [16]

    D., & Allamandola, L

    Boersma, C., Bregman, J. D., & Allamandola, L. J. 2013, ApJ, 769, 117

    work page 2013

  17. [17]

    L., Bauschlicher, C

    Boersma, C., Mattioda, A. L., Bauschlicher, C. W., et al. 2009, ApJ, 690, 1208

    work page 2009

  18. [18]

    Witteborn, F. C. 1989, ApJ, 344, 791

    work page 1989

  19. [19]

    2011, in EAS Publications Series, V ol

    Cami, J. 2011, in EAS Publications Series, V ol. 46, EAS Publications Series, 117–122

    work page 2011

  20. [20]

    P., Lequeux, J., & Verstraete, L

    Cesarsky, D., Jones, A. P., Lequeux, J., & Verstraete, L. 2000, A&A, 358, 708

    work page 2000

  21. [21]

    2023, ApJ, 944, L12

    Chastenet, J., Sutter, J., Sandstrom, K., et al. 2023, ApJ, 944, L12

    work page 2023

  22. [22]

    2011, ApJS, 196, 3 Article number, page 10 of 12 Maragkoudakis et al.: PDRs4All XVIII: PAH Ionisation and Size Across the Orion Bar

    Cheng, B.-M., Chen, H.-F., Lu, H.-C., et al. 2011, ApJS, 196, 3 Article number, page 10 of 12 Maragkoudakis et al.: PDRs4All XVIII: PAH Ionisation and Size Across the Orion Bar

    work page 2011

  23. [23]

    2024, A&A, 685, A75

    Chown, R., Sidhu, A., Peeters, E., et al. 2024, A&A, 685, A75

    work page 2024

  24. [24]

    A., Candian, A., Berné, O., & Tielens, A

    Croiset, B. A., Candian, A., Berné, O., & Tielens, A. G. G. M. 2016, A&A, 590, A26

    work page 2016

  25. [25]

    Draine, B. T. & Li, A. 2007, ApJ, 657, 810

    work page 2007

  26. [26]

    T., Li, A., Hensley, B

    Draine, B. T., Li, A., Hensley, B. S., et al. 2021, ApJ, 917, 3

    work page 2021

  27. [27]

    V ., Kreckel, K., Sandstrom, K

    Egorov, O. V ., Kreckel, K., Sandstrom, K. M., et al. 2023, ApJ, 944, L16

    work page 2023

  28. [28]

    P., Marshall, A

    Ekern, S. P., Marshall, A. G., Szczepanski, J., & Vala, M. 1998, Journal of Phys- ical Chemistry A, 102, 3498

    work page 1998

  29. [29]

    C., Tielens, A

    Galliano, F., Madden, S. C., Tielens, A. G. G. M., Peeters, E., & Jones, A. P. 2008, ApJ, 679, 310 García-Bernete, I., Rigopoulou, D., Alonso-Herrero, A., et al. 2022, A&A, 666, L5

    work page 2008

  30. [30]

    R., Pety, J., Cuadrado, S., et al

    Goicoechea, J. R., Pety, J., Cuadrado, S., et al. 2025, A&A, 696, A100

    work page 2025

  31. [31]

    R., Pety, J., Cuadrado, S., et al

    Goicoechea, J. R., Pety, J., Cuadrado, S., et al. 2016, Nature, 537, 207

    work page 2016

  32. [32]

    R., Santa-Maria, M

    Goicoechea, J. R., Santa-Maria, M. G., Bron, E., et al. 2019, A&A, 622, A91

    work page 2019

  33. [33]

    2024, A&A, 685, A73

    Habart, E., Peeters, E., Berné, O., et al. 2024, A&A, 685, A73

    work page 2024

  34. [34]

    Habing, H. J. 1968, Bull. Astron. Inst. Netherlands, 19, 421

    work page 1968

  35. [35]

    J., Reiter, M., O’Dell, C

    Haworth, T. J., Reiter, M., O’Dell, C. R., et al. 2023, MNRAS, 525, 4129

    work page 2023

  36. [36]

    N., Bosman, A

    Heays, A. N., Bosman, A. D., & van Dishoeck, E. F. 2017, A&A, 602, A105

    work page 2017

  37. [37]

    R., Jansen, D

    Hogerheijde, M. R., Jansen, D. J., & van Dishoeck, E. F. 1995, A&A, 294, 792

    work page 1995

  38. [38]

    2001, A&A, 370, 1030

    Hony, S., Van Kerckhoven, C., Peeters, E., et al. 2001, A&A, 370, 1030

    work page 2001

  39. [39]

    2018, A&A, 615, A129

    Joblin, C., Bron, E., Pinto, C., et al. 2018, A&A, 615, A129

    work page 2018

  40. [40]

    Joblin, C., Tielens, A. G. G. M., Allamandola, L. J., & Geballe, T. R. 1996, ApJ, 458, 610

    work page 1996

  41. [41]

    W., Ruhl, E., Baumgartel, H., Tobita, S., & Leach, S

    Jochims, H. W., Ruhl, E., Baumgartel, H., Tobita, S., & Leach, S. 1994, ApJ, 420, 307

    work page 1994

  42. [42]

    D., Campbell, M

    Kassis, M., Adams, J. D., Campbell, M. F., et al. 2006, ApJ, 637, 823

    work page 2006

  43. [43]

    2025, A&A, 699, A133

    Khan, B., Abbott, B., Peeters, E., et al. 2025, A&A, 699, A133

    work page 2025

  44. [44]

    J., Vacca, W

    Knight, C., Peeters, E., Stock, D. J., Vacca, W. D., & Tielens, A. G. G. M. 2021, ApJ, 918, 8

    work page 2021

  45. [45]

    Knight, C., Peeters, E., Tielens, A. G. G. M., & Vacca, W. D. 2022, MNRAS, 509, 3523

    work page 2022

  46. [46]

    Lai, T. S. Y ., Armus, L., Bianchin, M., et al. 2023, ApJ, 957, L26

    work page 2023

  47. [47]

    Lai, T. S. Y ., Armus, L., U, V ., et al. 2022, ApJ, 941, L36

    work page 2022

  48. [48]

    & Puget, J

    Leger, A. & Puget, J. L. 1984, A&A, 137, L5

    work page 1984

  49. [49]

    J., Candian, A., Huang, X., et al

    Mackie, C. J., Candian, A., Huang, X., et al. 2016, Journal of Chemical Physics, 145, 084313

    work page 2016

  50. [50]

    J., Candian, A., et al

    Maltseva, E., Mackie, C. J., Candian, A., et al. 2018, A&A, 610, A65

    work page 2018

  51. [51]

    D., & Allamandola, L

    Maragkoudakis, A., Boersma, C., Temi, P., Bregman, J. D., & Allamandola, L. J. 2022, ApJ, 931, 38

    work page 2022

  52. [52]

    2025, ApJ, 979, 90

    Maragkoudakis, A., Boersma, C., Temi, P., et al. 2025, ApJ, 979, 90

    work page 2025

  53. [53]

    2018, MNRAS, 481, 5370

    Maragkoudakis, A., Ivkovich, N., Peeters, E., et al. 2018, MNRAS, 481, 5370

    work page 2018

  54. [54]

    2020, MNRAS, 494, 642

    Maragkoudakis, A., Peeters, E., & Ricca, A. 2020, MNRAS, 494, 642

    work page 2020

  55. [55]

    L., Hudgins, D

    Mattioda, A. L., Hudgins, D. M., Boersma, C., et al. 2020, ApJS, 251, 22

    work page 2020

  56. [56]

    2018, A&A, 617, A77

    Parikka, A., Habart, E., Bernard-Salas, J., Köhler, M., & Abergel, A. 2018, A&A, 617, A77

    work page 2018

  57. [57]

    2024, A&A, 685, A77

    Pasquini, S., Peeters, E., Schefter, B., et al. 2024, A&A, 685, A77

    work page 2024

  58. [58]

    W., Allamandola, L

    Peeters, E., Bauschlicher, Jr., C. W., Allamandola, L. J., et al. 2017, ApJ, 836, 198

    work page 2017

  59. [59]

    2024, A&A, 685, A74

    Peeters, E., Habart, E., Berné, O., et al. 2024, A&A, 685, A74

    work page 2024

  60. [60]

    Peeters, E., Spoon, H. W. W., & Tielens, A. G. G. M. 2004, ApJ, 613, 986

    work page 2004

  61. [61]

    2015, A&A, 577, A16

    Pilleri, P., Joblin, C., Boulanger, F., & Onaka, T. 2015, A&A, 577, A16

    work page 2015

  62. [62]

    2012, A&A, 542, A69

    Pilleri, P., Montillaud, J., Berné, O., & Joblin, C. 2012, A&A, 542, A69

    work page 2012

  63. [63]

    Allamandola, L. J. 2012, ApJ, 754, 75

    work page 2012

  64. [64]

    R., García-Bernete, I., et al

    Rigopoulou, D., Donnan, F. R., García-Bernete, I., et al. 2024, arXiv e-prints, arXiv:2406.11415

    work page arXiv 2024

  65. [65]

    D., et al

    Salgado, F., Berné, O., Adams, J. D., et al. 2016, ApJ, 830, 118

    work page 2016

  66. [66]

    M., Bolatto, A

    Sandstrom, K. M., Bolatto, A. D., Bot, C., et al. 2012, ApJ, 744, 20

    work page 2012

  67. [67]

    A., Tielens, A

    Schutte, W. A., Tielens, A. G. G. M., & Allamandola, L. J. 1993, ApJ, 415, 397

    work page 1993

  68. [68]

    Shannon, M. J. & Boersma, C. 2018, in Proceedings of the 17th Python in Sci- ence Conference (SciPy), 99

    work page 2018

  69. [69]

    Smith, J. D. T., Draine, B. T., Dale, D. A., et al. 2007, ApJ, 656, 770

    work page 2007

  70. [70]

    J., Choi, W

    Stock, D. J., Choi, W. D.-Y ., Moya, L. G. V ., et al. 2016, ApJ, 819, 65

    work page 2016

  71. [71]

    Stock, D. J. & Peeters, E. 2017, ApJ, 837, 129

    work page 2017

  72. [72]

    Tielens, A. G. G. M. 2005, The Physics and Chemistry of the Interstellar Medium (Cambridge Univ. Press, Cambridge)

    work page 2005

  73. [73]

    Tielens, A. G. G. M., Meixner, M. M., van der Werf, P. P., et al. 1993, Science, 262, 86 Van De Putte, D., Meshaka, R., Trahin, B., et al. 2024, A&A, 687, A86 Van De Putte, D., Peeters, E., Gordon, K. D., et al. 2025, A&A, 701, A111

    work page 1993

  74. [74]

    Vicente, S., Berné, O., Tielens, A. G. G. M., et al. 2013, ApJ, 765, L38

    work page 2013

  75. [75]

    W., Uchida, K

    Werner, M. W., Uchida, K. I., Sellgren, K., et al. 2004, ApJS, 154, 309

    work page 2004

  76. [76]

    X., Maragkoudakis, A., & Peeters, E

    Zang, R. X., Maragkoudakis, A., & Peeters, E. 2022, MNRAS, 511, 5142

    work page 2022

  77. [77]

    M., et al

    Zhen, J., Castellanos, P., Paardekooper, D. M., et al. 2015, ApJ, 804, L7 1 NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035- 1000, USA; e-mail:alexandros.maragkoudakis@nasa.gov 2 Department of Physics & Astronomy, The University of Western

    work page 2015

  78. [78]

    15" 10" 05

    Road, Tangjia, Zhuhai 519000, Guangdong Province, China Article number, page 11 of 12 A&A proofs:manuscript no. OrionBar_pyPAHdb_R1 5h35m20.8s -5°25'20" 15" 10" 05" 00" DF3 DF2 DF1 IF 0.10 0.15 0.20 0.25 0.30 0.35 0.40 pyPAHdb Fig. A.1.The pyPAHdb modelling error (σ pyPAHdb ) map. Appendix A: pyPAHdb modelling error The pyPAHdb modelling error (σpyPAHdb )...

    work page 2018