HI within and around observed and simulated galaxy discs
Bibliographic record
Abstract
Extragalactic gas accretion and outflows driven by stellar and active galactic nucleus (AGN) feedback are expected to influence the distribution and kinematics of gas in and around galaxies. Atomic hydrogen (H I ) is an ideal tracer of these processes, and it is uniquely observable in nearby galaxies. Here we made use of wide-field (1° ×1°), spatially resolved (down to 22″), high-sensitivity (∼10 18 cm −2 ) H I observations of five nearby spiral galaxies with stellar mass of ∼5 × 10 10 M ⊙ , taken with the MeerKAT radio telescope. Four of these were observed as part of the MHONGOOSE survey. We characterise the main H I properties in regions of a few hundred kiloparsecs around the discs of these galaxies, and compare them with synthetic H I data from a sample of 25 similarly massive star-forming galaxies from the TNG50 (20) and FIRE-2 (5) suites of cosmological hydrodynamical simulations. Overall, the simulated systems have H I and molecular hydrogen (H 2 ) masses in good agreement with the observations, but only when a pressure-based H 2 recipe is employed. The other recipes that we tested overestimate the H 2 -to-H I mass fraction by up to an order of magnitude. On a local scale, we find two main discrepancies between the observed and simulated data. First, the simulated galaxies show a more irregular H I morphology than the observed galaxies, due to the presence of H I with column density < 10 20 cm −2 up to ∼100 kpc from the galaxy centre, even though they inhabit more isolated environments than the observed targets. Second, the simulated galaxies and in particular those from the FIRE-2 suite, feature more complex and overall broader H I line profiles than the observed galaxies. We interpret this as being due to the combined effect of stellar feedback and gas accretion, which lead to a large-scale gas circulation that is more vigorous than in the observed galaxies. Our results indicate that, with respect to the simulations, gentler processes of gas inflows and outflows are at work in the nearby Universe, leading to more regular and less turbulent H I discs.
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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 | 0.001 |
| 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 | 0.000 |
| 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".