An N-body/SPH study of isolated galaxy mass density profiles
Bibliographic record
Abstract
We investigate the evolution of mass density profiles in secular disc galaxy models, paying special attention to the development of a two-component profile from a single initial exponential disc free of cosmological evolution (i.e. no accretion or interactions). As the source of density profile variations, we examine the parameter space of the spin parameter, halo concentration, virial mass, disc mass and bulge mass, for a total of 162 simulations in the context of a plausible model of star formation and feedback. The isolated galaxy models are based on the method of Springel & White and were evolved using the N-body/SPH code gadget-2. The initially pure exponential discs have a minimum of 1.4 million particles and most models were evolved over a period of 10 Gyr. We find that the slope of the outer density profile is in close agreement with that of the initial profile and remains stable over time, whereas the inner density profile slope evolves considerably as a result of angular momentum redistribution. The evolution of the galaxy mass density profile, including the development of a two-component profile with an inner and outer segment, is controlled by the ratio of the disc mass fraction, md, to the halo spin parameter, λ. The location of the break between the two components and speed at which it develops is directly proportional to md/λ; the amplitude of the transition between the inner and outer regions is however controlled by the ratio of halo concentration to virial velocity. The location of the divide between the inner and outer profile does not change with time. The condition for a two-component profile is roughly md/λ≥ 1. While the development of a two-component density profile is coupled to bar formation, not all barred galaxies develop a two-component profile. A galaxy model showing a clear minimum Toomre Q, normally linked to a double exponential in the stellar profile, may never exhibit any two-component feature thus yielding a fully evolved pure exponential disc.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".