Satellites of simulated galaxies: survival, merging and their relationto the dark and stellar haloes
Bibliographic record
Abstract
We study the population of satellite galaxies formed in a suite of N-body/gasdynamical simulations of galaxy formation in a Λ cold dark matter universe. The simulations resolve nearly 10 most luminous satellites around each host, and probe systems up to six or seven magnitudes fainter than the primary. We find little spatial or kinematic bias between the dark matter and the satellite population. The radius containing half of all satellites is comparable to the half-mass radius of the dark matter component, and the velocity dispersion of the satellites is a good indicator of the virial velocity of the halo; σsat/Vvir∼ 0.9 ± 0.2. Applied to the Local Group, this result suggests that the virial velocity of the Milky Way and M31 might be substantially lower than the rotation speed of their disc components; we find VMWvir∼ 109 ± 22 km s−1 and VM31vir∼138 ± 35 km s−1, respectively, compared to VMWrot∼ 220 km s−1 and VM31rot∼ 260 km s−1.Although the uncertainties are large, it is intriguing that both estimates are significantly lower than expected from some semi-analytic models, which predict a smaller difference between Vvir and Vrot. The detailed kinematics of simulated satellites and dark matter are also in good agreement: both components show a steadily decreasing velocity dispersion profile and a mild radial anisotropy in their velocity distribution. By contrast, the stellar halo of the simulated galaxies, which consists predominantly of stellar debris from disrupted satellites, is kinematically and spatially distinct from the population of surviving satellites. This is because the survival of a satellite as a self-bound entity depends sensitively on mass and on time of accretion and surviving satellites are significantly biased toward low-mass systems that have been recently accreted by the galaxy. Our results support recent proposals for the origin of the systematic differences between stars in the Galactic halo and in Galactic satellites: the elusive ‘building blocks’ of the Milky Way stellar halo were on average more massive, and were accreted (and disrupted) earlier than the population of dwarfs that has survived self-bound until thepresent.
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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 | 0.001 | 0.005 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".