PDRs4All
Bibliographic record
Abstract
Context. The infrared universe is dominated by emission from polycyclic aromatic hydrocarbons (PAHs) observed as aromatic infrared bands (AIBs). JWST has produced a rich trove of information on these PAH signatures. Aims. We aim to investigate the photochemical evolution of PAHs in photodissociation regions (PDRs), focusing on their molecular edge structures across key zones, including the H II region, the ionization front, the atomic PDR, the dissociation front, and the molecular PDR. Methods. We utilized JWST’s MIRI-MRS observations of the Orion Bar for the PDRs4All JWST Early Release Science program. We investigated the spectral and spatial characteristics of 10–15 µm AIBs. Results. The AIBs at 10.6, 10.8, 11.0, 11.2, 12.0, 12.7, 13.5, 14.0, and 14.2 µm share large-scale spatial morphologies, peaking in the atomic PDR and gradually declining with distance from the PDR surface. Correlations between the AIBs reveal that they are largely carried by PAHs. Profile variations and subcomponents of the 11.2 and 12.0 µm AIBs reveal a carrier that behaves independently of PAHs, which we attribute to very small grains (VSGs) and/or PAH clusters. We ascribe the 11.0 and 11.207 µm AIBs, part of the 12.0 µm AIB, and the 12.7, 13.5, and 14.2 µm AIBs to CHoop modes and discuss their hydrogen-adjacency assignments. We propose that the 10.6, 10.8, and 14.0 µm AIBs do not arise from CHoop modes. We derived the relative amounts of solo, duo, trio, and quartet CH groups to infer the molecular structures. These suggest that PAHs are dominated by solo and trio CH groups throughout the PDR. We attribute the decrease in duo and quartet CH groups relative to the solo CH groups toward the PDR surface to the effects of photolysis of the labile hydrogens. Conclusions. The 10–15 µm AIBs are powerful probes of the PAH molecular structures. This study showcases the spatial and spectral variability in CHoop features due to photochemical processing of PAHs, and the differentiated spectral characteristics of PAHs and VSGs, in a prototypical PDR.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.108 | 0.056 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".