X‐Ray versus Optical Observations of Active Galactic Nuclei: Evidence for Large Grains?
Bibliographic record
Abstract
Recently, Maiolino et al. constructed a sample of active galactic nuclei for which both the reddening E ( B - V ) and the column density N H to the nucleus could be determined. For most of the galaxies in their sample, they found that E ( B - V )/ N H is substantially smaller than for the diffuse interstellar medium of our Galaxy. They asserted that either the dust-to-gas ratio is lower than in the Galaxy or the grains are so large that they do not extinct or redden efficiently in the optical. We show that there is no systematic increase in E ( B - V ) with N H for the Maiolino et al. galaxies, which suggests that the X-ray absorption and optical extinction occur in distinct media. In a later paper, Maiolino et al. suggested that the observed lines of sight for the previous Maiolino et al. galaxies pass through the "torus" that obscures the broad-line region and nuclear continuum in Seyfert 2 galaxies and argued that the torus grains are larger than Galactic grains. There is no reason to believe that the lines of sight for these galaxies pass through the torus, since the observed column densities are lower than those typically observed in Seyfert 2 galaxies. We suggest instead that the X-ray absorption occurs in material located off the torus and/or accretion disk, while the optical extinction occurs in material located beyond the torus. The X-ray absorbing material could either be dust-free or contain large grains that do not extinct efficiently in the optical. There is no conclusive evidence that the grains in active galactic nuclei are systematically larger than those in the diffuse interstellar medium of our Galaxy. We discuss an alternative way to probe the properties of dust in Seyfert tori but find that observations of Seyfert 2 nuclei with higher resolution than currently available will be needed in order to place stringent limits on the dust.
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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 | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".