The [C ii] emission as a molecular gas mass tracer in galaxies at low and high redshifts
Bibliographic record
Abstract
We present ALMA Band 9 observations of the [C ii]158 |$\mu$|m emission for a sample of 10 main-sequence galaxies at redshift |$z$| ∼ 2, with typical stellar masses (log M⋆/M⊙ ∼ 10.0–10.9) and star formation rates (∼35–115 M⊙ yr−1). Given the strong and well-understood evolution of the interstellar medium from the present to |$z$| = 2, we investigate the behaviour of the [C ii] emission and empirically identify its primary driver. We detect [C ii] from six galaxies (four secure and two tentative) and estimate ensemble averages including non-detections. The [C ii]-to-infrared luminosity ratio (|${\rm [C\, {\small II}]}$|/LIR) of our sample is similar to that of local main-sequence galaxies (∼2 × 10−3), and ∼10 times higher than that of starbursts. The [C ii] emission has an average spatial extent of 4–7 kpc, consistent with the optical size. Complementing our sample with literature data, we find that the [C ii] luminosity correlates with galaxies’ molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics: the [C ii]-to-H2 conversion factor (|$\alpha _{\rm [C\, {\small II}]} \sim 30$| M⊙/L⊙) is largely independent of galaxies’ depletion time, metallicity, and redshift. [C ii] seems therefore a convenient tracer to estimate galaxies’ molecular gas content regardless of their starburst or main-sequence nature, and extending to metal-poor galaxies at low and high redshifts. The dearth of [C ii] emission reported for |$z$| > 6–7 galaxies might suggest either a high star formation efficiency or a small fraction of ultraviolet light from star formation reprocessed by 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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".