Structural and Photometric Properties of the Andromeda Satellite Dwarf Galaxy Lacerta I from Deep Imaging with WIYN pODI
Bibliographic record
Abstract
Abstract We present results from WIYN pODI imaging of Lacerta I (And XXXI), a satellite dwarf galaxy discovered in the outskirts of the Andromeda galaxy (M31) in Pan-STARRS1 survey data. Our deep, wide-field <?CDATA $g,i$?> photometry reaches ∼3 mag fainter than the photometry in the Pan-STARRS1 discovery paper and allows us to trace the stellar population of Lac I beyond two half-light radii from the galaxy center. We measure a Tip of the Red Giant Branch distance for Lac I of <?CDATA ${(m-M)}_{0}=24.44\pm 0.11$?> mag (773 ± 40 kpc, or 264 ± 6 kpc from M31), which is consistent with the Pan-STARRS1 distance. We use a maximum-likelihood technique to derive structural properties for the galaxy, and find a half-light radius (r h ) of 3.24 ± 0.21 arcmin (728 ± 47 pc), ellipticity ( <?CDATA $\epsilon $?> ) of 0.44 ± 0.03, total magnitude M V = −11.4 ± 0.3, and central surface brightness <?CDATA ${\mu }_{V,0}=24.8\pm 0.3$?> mag arcsec−2. We find no H i emission in archival data and set a limit on Lac I’s neutral gas mass-to-light ratio of <?CDATA ${M}_{{\rm{H}}{\rm{I}}}/{L}_{V}$?> < 0.06 <?CDATA ${M}_{\odot }$?> / <?CDATA ${L}_{\odot }$?> , confirming Lac I as a gas-poor dwarf spheroidal galaxy. Photometric metallicities derived from Red Giant Branch stars within 2 r h yield a median [Fe/H] of −1.68 ± 0.03, which is more metal-rich than the spectroscopically derived value from Martin et al. Combining our measured magnitude with this higher metallicity estimate places Lac I closer to its expected position on the luminosity–metallicity relation for dwarf galaxies.
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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 | 0.000 |
| 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".