A search for H i 21 cm absorption towards a radio-selected quasar sample – II. A new low spin temperature DLA at high redshift
Bibliographic record
Abstract
We report results from a deep search for redshifted H i 21 cm absorption from eight damped Lyman α absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. H i 21 cm absorption was detected from the z = 2.192 DLA towards TXS 2039+187, only the sixth case of such a detection at z > 2, while upper limits on the H i 21 cm optical depth were obtained in six other DLAs at z > 2. Our detection of H i 21 cm absorption in the eighth system, at z = 2.289 towards TXS 0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted H i 21 cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its spin temperature Ts. For three non-detections of H i 21 cm absorption, we obtain strong lower limits on the spin temperature, Ts ≳ 790 K, similar to the bulk of the high-z DLA population; three other DLAs yield weak lower limits, Ts > 140–400 K. However, for the two DLAs with detections of H i 21 cm absorption, the derived spin temperatures are both low, Ts = (160 ± 35) × (f/0.35) K for the z = 2.192 DLA towards TXS 2039+187 and Ts = (72 ± 18) × (f/0.52) K for the z = 2.289 DLA towards TXS 0311+430. These are the first two DLAs at z > 1 with Ts values comparable to those obtained in local spiral galaxies. Based on the observed correlations between spin temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".