Tracing satellite planes in the Sculptor group
Bibliographic record
Abstract
Context. In recent years, a new generation of large-scale imaging surveys have probed wide field regions for the first time around some nearby galaxies in an unprecedentedly low surface-brightness regime (∼28.0−29.0 mag arcsec −2 ). This provides the chance to discover very faint dwarf satellites by means of systematic visual inspection of these public deep images. Aims. In this paper, we report the first results of a systematic survey of faint dwarf spheroidal galaxies in the vicinity of the bright late-type spiral galaxy NGC 253 by means of a visual inspection of the images taken by the Dark Energy Survey. Methods. We performed a new NGC 253 satellite search using co-added image cutouts reprocessed in the DESI Legacy image surveys. We used GALFIT software to investigate the photometric and structural properties of three dwarf galaxies. Results. We report the discovery of three new dwarf galaxies in the vicinity of the brightest member of the Sculptor filament, the late-type spiral NGC 253, located at a distance of 3.7 Mpc towards Anti-Virgo. We name them Do II, Do III, and Do IV. Assuming they are companions of NGC 253, their total absolute V -magnitudes fall in the −7 to −9 mag range, which is typical for dwarf satellites in the local Universe. The central surface brightness tends to be extremely low for all three discovered dwarfs and falls roughly in the range of 25−26 mag arcsec −2 in g -band. Using known data on distances and velocities of galaxies, we estimate the total virial mass of the NGC 253 group to be 8 × 10 11 M ⊙ , which gives a virial radius of R 200 = 186 kpc and a turn-around radius of 706 kpc. We also discuss the possible existence of a spatially flattened and velocity-correlated satellite system around NGC 253. This large-scale structure is orientated almost edge-on to the line of sight. The possible plane of satellites is only 31 kpc thick with a minor-to-major axis ratio of 0.14. Four out of five galaxies with measured velocities follow a common velocity trend similar to those observed in the planes of satellites around the Andromeda and Centaurus A galaxies. However, the small number of galaxies with known velocities prevents us from reaching a definitive conclusion about the formation scenario of the structure and its possible relation to the surrounding cosmic web.
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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 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".