The connection between star formation and metallicity evolution in barred spiral galaxies
Bibliographic record
Abstract
We have performed a series of chemodynamical simulations of barred disc galaxies. Our goal is to determine the physical processes responsible for the increase in the central gas-phase metallicity and of the central star formation rate (SFR) observed in the Sloan Digital Sky Survey (SDSS). All simulations start with an axisymmetric distribution of stars and gas, embedded into a spherical dark matter halo. We define a 2 kpc diameter central aperture to approximate the integrated spectroscopic fibre measurements from the SDSS. The chemical evolution observed within this central region depends critically upon the relative size of the bar and the aperture, which evolves strongly with time. At t ∼ 0.5 Gyr, a strong bar forms via a disc instability, whose length is considerably longer than the 2 kpc aperture. The stars and gas lose angular momentum and follow elongated orbits that cause an intense mixing of the gas between the central region and its surroundings. During the next 1.5 Gyr, the orbits of the stars inside the bar do not evolve much, but the orbits of the gas contract significantly until the entire gas bar is contained in the 2 kpc aperture, resulting in a net flux of gas into the central region. During this period, the metallicity in the central region increases steadily, and this enrichment is dominated by metal-rich gas that is flowing into the central region. The main result of this work is therefore that the observed enrichment in the centres of barred galaxies is not dominated by in situ enrichment by stars formed in the centre. Rather, star formation occurs along the full length of the bar, much of which occurs initially outside the 2 kpc aperture. About 50 per cent of the metals that end up in the central region originate from this extended bar-long star formation, but flow into the central region due to loss of angular momentum. The effect is less significant for iron because the delay for the onset of Type Ia supernovae leaves less time for mixing. Still, there is a significant increase in [Fe/H] before the central stars contribute to in situ enrichment. Eventually, as the orbits of the gas inside the bar contract, they fall completely inside the central region, and only then the central region can be regarded as a closed-box system. However, by that time, most of the metal enrichment in the central region has already taken place. We conclude that there is no direct connection between central SFR and central metallicity. The central metallicity does not originate exclusively from central stars. Instead, the global SFR (especially along the bar) and the large-scale flow of enriched gas play a major role.
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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 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".