PI REVIEW · ARCHIVE TRACK · NO NEW XMM TIME
At fixed projected radius and FUV surface brightness in M101's inner disk, do arm cells and interarm cells have different source-controlled diffuse X-ray surface brightness FUV coupling slopes ψAI? This is an archive-track question: no new XMM time requested, and no result is interpreted as a feedback mechanism or vertical position.
01 · The Question
At fixed projected radius and FUV surface brightness, does the spiral-arm environment in M101 change the coupling slope of diffuse X-ray surface brightness with FUV?
Kuntz & Snowden (2010, ApJS 188, 46) used ~1 Ms Chandra to establish M101's source-controlled diffuse X-ray power-law coupling with GALEX FUV (ΣX ∝ ΣFUVβ, β ≈ 0.55), and found an additive pedestal A(R) unrelated to recent star formation. But their stratification variable was radius, not arm state — "interarm" appears only once in 152,050 characters of text, in passing. Garner et al. (2024, ApJ 961, 217) published the full M101 arm/interarm mask construction method, but never applied it to X-ray/FUV coupling. I020 tests only a narrower premise: after controlling for radius, does the arm label change the coupling slope itself.
02 · Why It Matters
This would not overturn Kuntz & Snowden's radially-stratified coupling law; but it would limit its scope: in M101, radius alone does not absorb the arm-environment modulation of the coupling slope. Any resolved-feedback model that treats FUV–X-ray coupling as a pure function of radius must add a measured arm-phase term.
If the 95% interval falls entirely within ±δψ, the result only supports this one galaxy, this one archival depth, this one response domain — that the arm label does not change the coupling slope. It does not validate a general law for face-on spirals, nor prove the absence of arm-phase effects.
Luan & Wang (2025, ApJ 986, 167) did arm-phase-resolved diffuse spectral analysis in M51 with 1.3 Ms Chandra, finding higher average temperatures in arm regions — but that is temperature stratification, not FUV coupling slope, and GALEX FUV was only a comparison image, not a regression variable. Wezgowiec et al. (2021, MNRAS 508, 6155) did on-arm/off-arm spectral extraction in M83, but likewise did not fit an arm × FUV interaction coefficient. I020's estimand has not been precisely pre-empted in the literature (E6 screened with extended vocabulary, 0 pre-empting papers).
03 · What the Archive Actually Covers
Figures: 1-column PNG · 2-column PNG
The three M101-targeted ObsIDs (0104260101, 0212480201, 0824450501) have 15′ radius nominal FoVs extending to 15.63′, 17.94′, 21.16′, all covering Garner+2024's inner-disk boundary (430″ = 7.17′). But this is only nominal geometric coverage: clean GTIs, chip gaps, source masks, response qualification — all unresolved. This page does not claim the archive is sufficient to answer ψAI.
04 · What Is Actually Measured
Figures: 1-column PNG · 2-column PNG
ψAI = d² log(S) / dU dAi
The arm-minus-interarm difference in FUV coupling slope, defined on the FUV-coupled component S (not total surface brightness). Reported from the same frozen 95% CI [L, U]; not a temperature difference, not a level residual.
δψ > 0
No external threshold for an arm × FUV interaction coefficient exists in the literature (E5 confirmed structural absence). δψ must be generated by R6 injection-recovery under the Fork-B model, not back-calculated from Kuntz error bars.
All seven qualifications OPEN
E1 geometry, E2 source control, E3 response domain, E4 background/covariance, E5 δψ/recovery, E6 pre-emption, E7 pedestal P(R). Any single failure → INCONCLUSIVE.
05 · What the Answer Looks Like
Figures: 1-column PNG · 2-column PNG
| Outcome | Criterion | What Can Be Said | What Cannot Be Said |
|---|---|---|---|
| SUPPORT | L > δψ or U < −δψ | Arm environment materially changes the FUV coupling slope. | Not proof of feedback mechanism, mixing timescales, or vertical position. |
| WEAKEN | −δψ ≤ L ≤ U ≤ δψ | At this radius/depth/response domain, arm label does not change the coupling slope. | Does not exclude smaller effects, does not extrapolate to other galaxies. |
| INCONCLUSIVE | Interval overlaps boundary, non-finite, insufficient common support, recovery/coverage failure, or any qualification missing/failed | Acknowledge measurement did not establish. | Cannot infer physics from no-result. |
06 · If the Answer Is the Other Way
If the interval only contains zero, yet cannot fall within ±δψ, the most honest result is INCONCLUSIVE: the data neither excluded zero, nor pushed the residual below the materiality boundary. It does not move the credibility of "does the arm change the coupling slope"; this is precisely the branch I020 must preserve, not a packageable physical null.
The deeper risk is pedestal confusion: the additive offset A(R) quantified by Kuntz+Snowden2010 accounts for ~20% of ΣX in the 1′–3′ annuli. If P(R) ≥ 0 is not explicitly included in the model, an arm/interarm level difference would fake ψAI ≈ 0.034–0.074 (34–74% of δψ ~ 0.10), biased toward SUPPORT. The Fork-B design (I020-G1-S1) was frozen precisely to eliminate this bias.
07 · Cost and Unknowns
08 · Reproducibility
| Item | Actual Command Run / Fixed Input This Time | Conclusion Boundary |
|---|---|---|
| XMM archive | cycles/cycle-obs9/presenter_i226/publication-v2/source/archive_retrieval/raw/xsa_v_all_observations.csv (XSA TAP v_all_observations, 7 rows) | 179.283 ks is observation duration, not clean time or source exposure. |
| Kuntz+Snowden2010 β / A(R) | cycles/cycle-5/materials/I020_R3_D049_ads_preemption/Kuntz2010_IOP_article.txt (Table 9, A≥0 block) | β = 0.59/0.49/0.56 are design inputs, not I020 measurements. |
| Garner+2024 mask | shared/sources/m101-diffuse-xray-fuv-coupling.md §T255 | Method published, products unretrievable; Hα width rule has circularity risk. |
| Display figures | DSS2 color and ESDC/P/XMM/EPIC-RGB HiPS2FITS, CRVAL=M101; original FITS, scripts, hash, and clean replay in the publication manifest with this page. | Display stretch ≠ exposure correction ≠ scientific flux. |
Local evidence used on this page: I020 idea file, I020-G1-S1 preregistration, R3 evidence (idea-I020.md), M101 survey, source page m101-diffuse-xray-fuv-coupling.md. Static bundle manifest, figure replay, and bundle replay saved with this release; public page does not replace these canonical records.
