From stellar haloes to intracluster light: the physics of the Intra-Halo Stellar Component in cosmological hydrodynamical simulations
Bibliographic record
Abstract
ABSTRACT We study the Intra-Halo Stellar Component (IHSC) of Milky Way-mass systems up to galaxy clusters in the Horizon-AGN cosmological hydrodynamical simulation. We identify the IHSC using an improved phase-space galaxy finder algorithm which provides an adaptive, physically motivated, and shape-independent definition of this stellar component, that can be applied to haloes of arbitrary masses. We explore the IHSC mass fraction – total halo’s stellar mass, $f_{M_{*,\mathrm{IHSC}}} - M_{*}$, relation, and the physical drivers of its scatter. We find that on average, the $f_{M_{*,\mathrm{IHSC}}}$ increases with total stellar mass, with the scatter decreasing strongly with mass from 2 dex at $M_{*,\mathrm{tot}}\simeq 10^{11}\, \mathrm{M}_\odot$ to 0.3 dex at group masses. At high masses, $M_{*,\mathrm{tot}}\gt 10^{11.5}\, \mathrm{M}_\odot$, $f_{M_{*,\mathrm{IHSC}}}$ increases with the number of substructures, and with the mass ratio between the central galaxy and largest satellite, at fixed M*, tot. From mid-size groups and systems below $M_{*,\mathrm{tot}}\lt 10^{12}\, \mathrm{M}_\odot$, we find that the central galaxy’s stellar rotation-to-dispersion velocity ratio, V/σ, displays the strongest (anti)-correlation with $f_{M_{*,\mathrm{IHSC}}}$ at fixed M*, tot of all the galaxy and halo properties explored, transitioning from $f_{M_{*,\mathrm{IHSC}}}\lt 0.1$ per cent for high V/σ, to $f_{M_{*,\mathrm{IHSC}}}\approx 5$ per cent for low V/σ galaxies. By studying the $f_{M_{*,\mathrm{IHSC}}}$ temporal evolution, we find that, in the former, mergers not always take place, but if they did, they happened early (z > 1), while the high $f_{M_{*,\mathrm{IHSC}}}$ population displays a much more active merger history. In the case of massive groups and galaxy clusters, $M_{*,\mathrm{tot}}\gtrsim 10^{12}\, \mathrm{M}_\odot$, a fraction $f_{M_{*,\mathrm{IHSC}}}\approx 10-20$ per cent is reached at z ≈ 1 and then they evolve across lines of constant $f_{M_{*,\mathrm{IHSC}}}$ modulo some small perturbations. Because of the limited simulation’s volume, the latter is only tentative and requires a larger sample of simulated galaxy clusters to confirm.
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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 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| 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".