Two-dimensional Hα kinematics of bulgeless disc galaxies
Bibliographic record
Abstract
We present two-dimensional Hα velocity fields for 20 late-type, disc-dominated spiral galaxies, the largest sample to date with high-resolution Hα velocity fields for bulgeless discs. From these data, we derive rotation curves and the location of the kinematic centres. The galaxy sample was selected to contain nucleated and non-nucleated galaxies (as determined from prior Hubble Space Telescope imaging), which allows us to investigate what impact the gas kinematics in the host disc have on the presence (or absence) of a nuclear star cluster. In general, we find that the velocity fields span a broad range of morphologies. While some galaxies show regular rotation, most have some degree of irregular gas motions, which in nearly all cases either can be attributed to the presence of a bar or is connected to a rather patchy distribution of the Hα emission and the stellar light. There appears to be no systematic difference in the kinematics of nucleated and non-nucleated discs. Due to the large fields of view of the integral field units we use, we are able to observe the flattening of the rotation curve in almost all of our sample galaxies. This makes modelling of the velocity fields relatively straightforward. Due to the complexities of the velocity fields, we obtain reliable determinations of the kinematic centre for only six of our 20 sample galaxies. For all of these, the locations of the nuclear star cluster/photometric centre and the kinematic centre agree within the uncertainties. These locations also agree for seven more objects, despite considerably larger uncertainties as to the accuracy of the kinematic centre. If we disregard all kinematically irregular galaxies, our study concludes that nuclear star clusters truly occupy the nuclei, or dynamical centres, of their hosts. Our results are thus consistent with in situ formation of nuclear star clusters. Yet, many well-motivated formation scenarios for nuclear clusters invoke off-centre cluster formation and subsequent sinking of clusters due to dynamical friction. In that case, our results imply that dynamical friction in the centres of bulgeless galaxies must be very effective in driving massive clusters to the kinematic centre.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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".