GALAXY STELLAR MASS ASSEMBLY BETWEEN 0.2 <<i>z</i>< 2 FROM THE S-COSMOS SURVEY
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Bibliographic record
Abstract
We follow the galaxy stellar mass assembly by morphological and spectral type in the COSMOS 2 deg^2 field. We derive the stellar mass functions and stellar mass densities from z = 2 to z = 0.2 using 196,000 galaxies selected at F_(3.6 μm) > 1 μJy with accurate photometric redshifts (σ_[(zphot−zspec)]/(1+zspec) = 0.008 at i^+ < 22.5). Using a spectral classification, we find that z ~ 1 is an epoch of transition in the stellar mass assembly of quiescent galaxies. Their stellar mass density increases by 1.1 dex between z = 1.5-2 and z = 0.8-1 (Δt ~ 2.5 Gyr), but only by 0.3 dex between z = 0.8-1 and z ~ 0.1 (Δt ~ 6 Gyr). Then, we add the morphological information and find that 80%-90% of the massive quiescent galaxies (logM ~ 11) have an elliptical morphology at z < 0.8. Therefore, a dominant mechanism links the shutdown of star formation and the acquisition of an elliptical morphology in massive galaxies. Still, a significant fraction of quiescent galaxies present a Spi/Irr morphology at low mass (40%-60% at logM ~ 9.5), but this fraction is smaller than predicted by semi-analytical models using a "halo quenching" recipe. We also analyze the evolution of star-forming galaxies and split them into "intermediate activity" and "high activity" galaxies. We find that the most massive "high activity" galaxies end their high star formation rate phase first. Finally, the space density of massive star-forming galaxies becomes lower than the space density of massive elliptical galaxies at z < 1. As a consequence, the rate of "wet mergers" involved in the formation of the most massive ellipticals must decline very rapidly at z < 1, which could explain the observed slow down in the assembly of these quiescent and massive sources.
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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 | 0.001 | 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 | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.002 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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