MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES
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Bibliographic record
Abstract
We compare molecular gas traced by 12 CO (2–1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between Σ mol and Σ SFR but also find important second-order systematic variations in the apparent molecular gas depletion time, . At the 1 kpc common resolution of HERACLES, CO emission correlates closely with many tracers of the recent SFR. Weighting each line of sight equally, using a fixed α CO equivalent to the Milky Way value, our data yield a molecular gas depletion time, Gyr with 0.3 dex 1σ scatter, in very good agreement with recent literature data. We apply a forward-modeling approach to constrain the power-law index, N , that relates the SFR surface density and the molecular gas surface density, . We find N = 1 ± 0.15 for our full data set with some scatter from galaxy to galaxy. This also agrees with recent work, but we caution that a power-law treatment oversimplifies the topic given that we observe correlations between and other local and global quantities. The strongest of these are a decreased in low-mass, low-metallicity galaxies and a correlation of the kpc-scale with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H 2 conversion factor (α CO ) that depends on dust shielding, and thus D/G, in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes this the most conservative explanation of the strongest observed trends. After applying a D/G-dependent α CO , some weak correlations between and local conditions persist. In particular, we observe lower and enhanced CO excitation associated with nuclear gas concentrations in a subset of our targets. These appear to reflect real enhancements in the rate of star formation per unit gas, and although the distribution of τ dep does not appear bimodal in galaxy centers, τ dep does appear multivalued at fixed Σ H2 , supporting the idea of "disk" and "starburst" modes driven by other environmental parameters.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| 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 it