WALLABY: an untargeted search for H <scp>i</scp> -bearing ultra-diffuse galaxies uncovers the first known ultra-diffuse galaxy pair
Bibliographic record
Abstract
ABSTRACT Using the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY), we performed an untargeted search for H i-bearing ultra-diffuse galaxies (UDGs). We identified a core sample of 10 UDGs defined by $\mu _{0,g}\ge 24$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.5$ kpc, and a broader sample including 12 additional faint diffuse galaxies ($\mu _{0,g}\ge 23.7$ mag arcsec$^{-2}$ and $R_{\rm e}\ge 1.3$ kpc). Within the core sample, we highlight the first discovery of a pair of UDGs. Their projected separation is just 75 arcsec (22 kpc at 61.9 Mpc), with a central H i velocity difference of 34 km s$^{-1}$. The north-western UDG (WALLABY J104513−262755-UDG-1) has a larger H i reservoir, $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.95\pm 0.03$, compared with the south-eastern UDG (WALLABY J104513−262755-UDG-2), $\log _{10}(M_{\rm H\, {\small I}}/\rm {\rm M}_{\odot }) = 8.60\pm 0.04$. The stellar mass and star formation rate of UDG-1 are also approximately an order of magnitude larger at $\log _{10}(M_*/\rm {\rm M}_{\odot }) = 8.07\pm 0.12$ and $\log _{10}({\rm SFR}/{\rm M}_{\odot}\,{\rm yr}^{-1}) = -1.26\pm 0.12$, respectively. The pair has an isolated local environment, with no other galaxies or H i sources within 30 arcmin (525 kpc) and $\pm 1000$ km s$^{-1}$. However, in the context of the larger-scale structure, the pair is located outside the virial radius of the Hydra cluster, with its position on the phase-space diagram indicating that it is infalling into the cluster. The identification of this H i-bearing UDG pair raises important questions around the formation of such a unique system and the evolution of UDGs in a transitional phase before ram pressure stripping and cluster infall.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.002 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".