The Optical-Infrared Colors of CORALS QSOs: Searching for Dust Reddening Associated with High-Redshift Damped Lyα Systems
Bibliographic record
Abstract
The presence of dust in quasar absorbers, such as damped Lyα (DLA) systems, may cause the background QSO to appear reddened. We investigate the extent of this potential reddening by comparing the optical-to-infrared colors of QSOs with and without intervening absorbers. Our QSO sample is based on the Complete Optical and Radio Absorption Line System (CORALS) survey of Ellison and coworkers. The CORALS data set consists of 66 radio-selected QSOs at z em ≥ 2.2 with complete optical identifications. We have obtained near-simultaneous B - and K -band magnitudes for a subset of the CORALS sample and supplemented our observations with further measurements published in the literature. In total, we have B - K colors for 42 of the 66 QSOs, of which 14 have intervening DLA systems. To account for redshift-related color changes, the B - K colors are normalized using the Sloan Digital Sky Survey QSO composite. The mean normalized B - K color of the DLA subsample is +0.12, whereas the mean for the no-DLA sample is -0.10; both distributions have rms scatters of ∼0.5. Neither a Student's t -test nor a Kolmogorov-Smirnov test indicate that there is any significant difference between the two color distributions. Based on simulations that redden the colors of QSOs with intervening DLA systems, we determine a reddening limit that corresponds to E ( B - V ) < 0.04 (SMC-like extinction) at 99% confidence (3 σ), assuming that E ( B - V ) is the same for all DLA systems. Finally, we do not find any general correlation between absorber properties (such as [Fe/Zn] or neutral hydrogen column density) and B - K color. The two reddest QSOs with DLA systems in our sample have H I column densities that differ from each other by an order of magnitude and moderate gas-to-dust ratios as inferred from chemical abundances. One of these two QSOs shows evidence for strong associated absorption from X-ray observations, an alternative explanation for its very red color. We conclude that the presence of intervening galaxies causes a minimal reddening of the background QSO.
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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 | 0.001 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".