Bibliographic record
Abstract
We present new K-band spectroscopy for a sample of 48 starburst galaxies, obtained using UKIRT in Hawaii. This constitutes a fair sample of the most common types of starburst galaxies found in the nearby Universe, containing galaxies with different morphologies, masses and metallicities, with far-infrared luminosity LIR<1010 L⊙. The variety of near-infrared spectral features shown by these galaxies implies different bursts characteristics, which suggests that we survey galaxies with different star formation histories or at different stages of their burst evolution. Using synthetic starburst models, we conclude that the ensemble of parameters that best describes starburst galaxies in the nearby Universe is a constant rate of star formation, a Salpeter initial mass function (IMF) with an upper mass cut-off of Mup=30 M⊙ and bursts ages between 10 Myr and 1 Gyr. The model is fully consistent with the differences observed in the optical and far-infrared (FIR) between the different types of starbursts. It suggests that H ii galaxies have younger bursts and lower metallicities than starburst nucleus galaxies (SBNGs), while luminous infrared galaxies (LIRGs) have younger bursts but higher metallicities. Although the above solution from the synthetic starburst model is fully consistent with our data, it may not constitute a strong constraint on the duration of the bursts and the IMF. A possible alternative may be a sequence of short bursts (which may follow an universal IMF) over a relatively long period of time. In favour of the multiple-burst hypothesis, we distinguish in our spectra some variations of near-infrared (NIR) features with the aperture that can be interpreted as evidence that the burst regions are not homogeneous in space and time. We also found that the burst stellar populations are dominated by early-type B stars, a characteristic which seems difficult to explain with only one evolved burst. Our observations suggest that the starburst phenomenon must be a sustained or self-sustained phenomenon: either star formation is continuous in time, or multiple bursts happen in sequence over a relatively long period of time. The generality of our observations implies that this is a characteristic of starburst galaxies in the nearby Universe.
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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 | 0.001 |
| 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) | 0.001 | 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".