Observations of carbon radio recombination lines with the NenuFAR telescope
Bibliographic record
Abstract
Context. Carbon radio recombination lines (CRRLs) at decametre wavelengths trace the diffuse phase of the interstellar medium (ISM) of the Galaxy. Observations of these lines allow for physical parameters of this phase to be measured. Aims. We observed CRRLs with the recently commissioned New Extension in Nançay Upgrading LOFAR (NenuFAR) telescope towards two of the brightest sources at low-frequency (10–85 MHz): Cassiopeia A and Cygnus A (hereafter, Cas A and Cyg A, respectively). We then measured the density, ne, and temperature, Te, of the electrons in line-of-sight clouds. Methods. We used NenuFAR’s beam-forming mode and integrated several tens of hours on each source. The nominal spectral resolution was 95.4 Hz. We developed a reduction pipeline primarily aimed at removing the radio frequency interference (RFI) contamination and correcting the baselines. We then performed a first fitting of the spectral lines observed in absorption associated with the line-of-sight clouds. Results. Cas A is the brightest source in the sky at low frequencies and represents an appropriate test bench for this new telescope. On this source, we detected 398 Cα lines between the principal quantum numbers n = 426 and n = 826. Cyg A is also a bright source, however, the Cα lines were observed to be fainter. We stacked the signal by groups of a few tens of lines to improve the quality of our fitting process. For both sources, we reached a significantly higher signal-to-noise ratio (S/N) and spectral resolution than the most recent detections by the LOw Frequency ARray (LOFAR). The variation of the spectral line widths with the electronic quantum number provides constraints on the physical properties of the clouds: Te, ne, and the temperature, T0, of the radiation field, the mean turbulent velocity, νt, and the typical size of the cloud. Conclusions. Our final constraints differ from those inferred from LOFAR results, with ∼50% lower Te, ∼35% lower ne, and from 10 to 80% higher νt, on average. The NenuFAR observations sample a larger space volume than LOFAR’s towards the same sources due to the differences in instrumental beam sizes. These discrepancies highlight the sensitivity of low-frequency CRRLs as probes of the diffuse ISM, paving the way towards large area surveys of CRRLs in our Galaxy.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| 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 | 0.001 |
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".