From star-forming spirals to passive spheroids: integral field spectroscopy of E+A galaxies
Bibliographic record
Abstract
We present three-dimensional spectroscopy of 11 E+A galaxies at z= 0.06–0.12. These galaxies were selected for their strong Hδ absorption but weak (or non-existent) [O ii] λ3727 and Hα emission. This selection suggests that a recent burst of star formation was triggered but subsequently abruptly ended. We probe the spatial and spectral properties of both the young (≲1 Gyr) and old (≳few Gyr) stellar populations. Using the Hδ equivalent widths we estimate that the burst masses must have been at least 10 per cent by mass (Mburst≳ 1010 M⊙), which is also consistent with the star formation history inferred from the broad-band spectral energy distributions. On average the A stars cover ∼33 per cent of the galaxy image, extending over 2–15 kpc2, indicating that the characteristic E+A signature is a property of the galaxy as a whole and not due to a heterogeneous mixture of populations. In approximately half of the sample, we find that the A stars, nebular emission and continuum emission are not co-located, suggesting that the newest stars are forming in a different place than those that formed ≲1 Gyr ago, and that recent star formation has occurred in regions distinct from the oldest stellar populations. At least 10 of the galaxies (91 per cent) have dynamics that class them as ‘fast rotators’ with magnitudes, v/σ, λR and bulge-to-total (B/T) ratio comparable to local, representative ellipticals and S0s. We also find a correlation between the spatial extent of the A stars and the dynamical state of the galaxy such that the fastest rotators tend to have the most compact A star populations, providing new constraints on models that aim to explain the transformation of later type galaxies into early types. Finally, we show that there are no obvious differences between the line extents and kinematics of E+A galaxies detected in the radio (active galactic nucleus, AGN) compared to non-radio sources, suggesting that AGN feedback does not play a dramatic role in defining their properties, and/or that its effects are short.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".