H <scp>i</scp> absorption at <i>z</i> ∼ 0.7 against the lobe of the powerful radio galaxy PKS 0409−75
Bibliographic record
Abstract
ABSTRACT We present results from a search for the H i 21-cm line in absorption towards 16 bright radio sources with the six-antenna commissioning array of the Australian Square Kilometre Array Pathfinder. Our targets were selected from the 2-Jy sample, a flux-limited survey of the southern radio sky with extensive multiwavelength follow-up. Two sources were detected in H i absorption including a new detection towards the bright Fanaroff–Riley Type II radio galaxy PKS 0409−75 at a redshift of $z$ = 0.674. The H i absorption line is blueshifted by ∼3300 km s−1 compared to the optical redshift of the host galaxy of PKS 0409−75 at $z$ = 0.693. Deep optical imaging and spectroscopic follow-up with the GMOS instrument on the Gemini-South telescope reveal that the H i absorption is associated with a galaxy in front of the southern radio lobe with a stellar mass of 3.2–6.8 × 1011 M⊙, a star formation rate of ∼1.24 M⊙ yr−1, and an estimated H i column density of 2.16 × 1021 cm−2, assuming a spin temperature of Tspin = 500 K and source covering factor of Cf = 0.3. Using polarization measurements of PKS 0409−75 from the literature, we estimate the magnetic field of the absorbing galaxy to be ∼14.5 $\mu$G, consistent with field strengths observed in nearby spiral galaxies but larger than expected for an elliptical galaxy. Results from this pilot study can inform future surveys as new wide-field telescopes allow us to search for 21-cm H i absorption towards all bright radio sources as opposed to smaller targeted samples.
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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 | 0.000 |
| 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) | 0.003 | 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".