HISTORY OF GALAXY INTERACTIONS AND THEIR IMPACT ON STAR FORMATION OVER THE LAST 7 Gyr FROM GEMS
Bibliographic record
Abstract
We perform a comprehensive estimate of the frequency of galaxy mergers and their impact on star formation over z ∼ 0.24–0.80 (lookback time T b ∼ 3–7 Gyr) using ∼3600 ( M ⩾ 1 × 10 9 M ☉ ) galaxies with GEMS Hubble Space Telescope , COMBO-17, and Spitzer data. Our results are as follows. (1) Among ∼790 high-mass ( M ⩾ 2.5 × 10 10 M ☉ ) galaxies, the visually based merger fraction over z ∼ 0.24–0.80, ranges from 9% ± 5% to 8% ± 2%. Lower limits on the major merger and minor merger fraction over this interval range from 1.1% to 3.5%, and 3.6% to 7.5%, respectively. This is the first, albeit approximate, empirical estimate of the frequency of minor mergers over the last 7 Gyr. Assuming a visibility timescale of ∼0.5 Gyr, it follows that over T b ∼ 3–7 Gyr, ∼68% of high-mass systems have undergone a merger of mass ratio >1/10, with ∼16%, 45%, and 7% of these corresponding respectively to major, minor, and ambiguous "major or minor" mergers. The average merger rate is ∼ a few × 10 −4 galaxies Gyr −1 Mpc −3 . Among ∼2840 blue-cloud galaxies of mass M ⩾ 1.0 × 10 9 M ☉ , similar results hold. (2) We compare the empirical merger fraction and merger rate for high-mass galaxies to three Λ cold dark matter-based models: halo occupation distribution models, semi-analytic models, and hydrodynamic SPH simulations. We find qualitative agreement between observations and models such that the (major+minor) merger fraction or rate from different models bracket the observations, and show a factor of 5 dispersion. Near-future improvements can now start to rule out certain merger scenarios. (3) Among ∼3698 M ⩾ 1.0 × 10 9 M ☉ galaxies, we find that the mean star formation rate (SFR) of visibly merging systems is only modestly enhanced compared to non-interacting galaxies over z ∼ 0.24–0.80. Visibly merging systems only account for a small fraction (<30%) of the cosmic SFR density over T b ∼ 3–7 Gyr. This complements the results of Wolf et al. over a shorter time interval of T b ∼ 6.2–6.8 Gyr, and suggests that the behavior of the cosmic SFR density over the last 7 Gyr is predominantly shaped by non-interacting galaxies.
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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 | 0.002 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".