The Secular Evolution of Disk Structural Parameters
Bibliographic record
Abstract
We present a comprehensive series of simulations to study the secular evolution of disk galaxies expected in a ΛCDM universe. Our simulations are organized in a hierarchy of increasing complexity, ranging from rigid-halo collisionless simulations to fully live simulations with gas and star formation. Our goal is to examine which structural properties of disk galaxies may result from secular evolution rather than from hierarchical assembly. In the vertical direction, we find that various mechanisms lead to heating, the strongest of which is the buckling instability of a bar, which leads to peanut-shaped bulges; these can be recognized face-on even in the presence of gas. We find that bars are robust structures that survive buckling and require a large (~20% of the total mass of the disk) central mass concentration to be destroyed. This can occur in dissipative simulations, where bars induce strong gas inflows, but requires that radiative cooling overcome heating. We show how angular momentum redistribution leads to increasing central densities and disk scale lengths and to profile breaks at large radii. The breaks in these simulations are in excellent agreement with observations, even when the evolution is collisionless. Disk scale lengths increase even when the total disk angular momentum is conserved; thus, mapping halo angular momenta to scale lengths is nontrivial. A decomposition of the resulting profile into a bulge+disk gives structural parameters in reasonable agreement with observations although kinematics betrays their bar nature. These findings have important implications for galaxy formation models, which have so far ignored or introduced in a very simplified way the effects of nonaxisymmetric instabilities on the morphological evolution of disk 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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".