XMM-Proposal-Agent v3-obs · cycle-obs9 · idea I091

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M51 arm-phase-controlled azimuthal tidal-axis contrast

Does the M51 disk X-ray emission along the NGC 5195 interaction axis (PA ≈ 15.4°) exceed what the disk's own arm/interarm structure predicts? An archive test with an explicit arm-phase-matched control — the origin discriminator that the prior family (I060/I081/I082) could not supply

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Snapshot 2026-08-25 · idea file shared/ideas/I091_m51-disk-azimuthal-tidal-axis-contrast-fork.md> · parent I082 · executed successor I097 · currently parked_hold> per R5 adjudication

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The question

In the M51–NGC 5195 interacting pair, does the soft diffuse X-ray emission along the interaction axis (PA ≈ 15.4°, from M51 toward NGC 5195) exceed what the disk's own arm-phase structure predicts at the same galactocentric radius — or is the disk emission arm-phase-dominated with no detectable tidal-axis excess

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That is a single number per sub-region, repeated at three galactocentric radii inside M51's optical disk

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ΔEMdisk>(φaxis>, ri>) = EM(Bi>) − EM(Ci

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where Bi> is a 30° wedge at PA ≈ 15.4° at radius ri> from the M51 nucleus, and Ci> is a conjugate wedge at the same ri> in a non-axis azimuth with the same arm-phase class> as Bi> (arm crest, interarm, or arm-interarm boundary, from the Luan & Wang 2025 18-region log-spiral phase decomposition or the Kuntz+2016 Chandra arm/interarm mask). The vector of ΔEMdisk> across i = 1, 2, 3 at r = 0.5–1.0′ / 1.0–1.5′ / 1.5–2.0′ is the azimuthal tidal-axis contrast profile

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Why anyone should care

The prior family — I060, I081, I082 — asked the same question but with an estimand that lacked an origin discriminator>. The B-minus-C contrast was confounded by ordinary M51 disk emission because both B and C sat inside M51's optical disk (D25) and the control had no arm-phase matching. A monotonic B-minus-C profile could arise from ordinary arm brightness decline under the same observable as the proposed "tidally displaced" or "tidally enhanced" labels

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The geometric constraint is permanent: the D25 regions of M51 (semi-axes 5.6′ × 3.45′ at PA = 163°) and NGC 5195 (semi-axis 2.39′) overlap by 2.60 arcmin along PA = 15.4°>. There is no> radial range along the inter-galaxy axis that is outside both galaxies' D25. Deterministic geometry replay (SHA-256 c5832864…>, clean-replay verified, see cycles/cycle-obs9/materials/R4_I082_terra_anchor_checks_v2.json>):

> >>ead> >>> >>> >>> >>> >>> >>>
QuantityValueSource
M51 → NGC 5195 separation4.4102 arcminSIMBAD J2000, both nuclei
M51 → NGC 5195 PA15.3740°astropy SkyCoord.position_angle
M51 D25 radius at PA = 15.4°4.6209 arcminD25 isophotal semi-axes 5.6′ × 3.45′ at PA = 163°
NGC 5195 D25 radius2.3946 arcminRC3 isophotal semi-axis
D25 overlap along axis2.6052 arcminsep − rD25,M51> − rD25,N5195> < 0
B1/B2/B3 max projected D25 q0.060 / 0.135 / 0.240all << 1 → all inside M51 D25

So I091 accepts the geometric impossibility of a D25-free axial region and reframes the question. The arm-phase control is the origin discriminator: if the tidal-axis direction shows excess EM beyond what arm-phase predicts, the residual is a candidate tidal component; if no excess, disk emission is arm-phase-dominated with no detectable tidal contribution. Both outcomes move credence — TIDAL-EXCESS raises credence that tidal interactions enhance hot gas emission along the interaction axis beyond the disk's natural azimuthal structure; ARM-PHASE-CONSISTENT bounds the observable tidal contribution to the disk X-ray emission

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Whose published conclusion changes> the I060/I081/I082 family (cycle-obs9, R2/hermes, archived). I082's surviving R4 sub-claim was "What is the source-masked M51 disk EM contrast along PA ≈ 15.4° relative to explicitly matched disk-phase controls?" — but no arm-phase control was operative in I082. I091 makes that control operative. A TIDAL-EXCESS result would be the first arm-phase-controlled evidence for a tidal-axis-associated X-ray enhancement in a face-on system; an ARM-PHASE-CONSISTENT result would bound the tidal contribution; a MIXED/COMPLEX result would constrain single-component tidal-response models

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What the measurement would look like

Three preregistered outcomes for the arm-phase-controlled azimuthal contrast
Three preregistered outcomes for ΔEMdisk>(φaxis>, r). The fourth outcome (INCONCLUSIVE) is reserved exclusively for recovery-target failure and is not a physical result. The shaded band is an illustrative ±1σ noise envelope; the actual threshold is calibrated by the E1 recovery simulation from actual archival clean exposure

The four outcomes are MR01-compliant and mutually exclusive

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  1. TIDAL-EXCESS> — ΔEMdisk> > 0 at ≥ 2 of 3 radii at the simulation-calibrated threshold, with the excess not attributable to arm-phase mismatch. Consistent with a tidally enhanced emission component along the interaction axis, beyond what the disk's arm-phase structure predicts
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  2. ARM-PHASE-CONSISTENT> — ΔEMdisk> consistent with zero at all radii after arm-phase matching, or the axial direction's EM fully explained by its arm-phase class. This is a positive> outcome: it bounds the tidal contribution to the disk X-ray emission above the sensitivity floor
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  3. MIXED/COMPLEX> — ΔEMdisk> is non-monotonic, or significant at only 1 of 3 radii, or the arm-phase control is ambiguous (Bi> sits on an arm-interarm boundary that cannot be uniquely classified). Also a positive> outcome: it reports a complex/mixed morphology that constrains both classes of models
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  4. INCONCLUSIVE> — reserved exclusively for recovery-target failure: (a) E3 fails (no qualifying arm-phase-matched C at any sub-region radius), (b) E1 recovery simulation shows the contrast is not measurable at the archival depth, (c) E9 arm-phase model cannot be constructed from existing data, or (d) E8 sub-region spectral commensurability fails. A null result (no detectable excess at any sub-region, but recovery passes) is not> INCONCLUSIVE — it is reported as ARM-PHASE-CONSISTENT
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What it looks like if the answer comes out the other way

If the result is ARM-PHASE-CONSISTENT>, the disk X-ray emission is arm-phase-dominated with no detectable tidal contribution along the axis. This is a positive> outcome — it bounds the observable tidal-enhancement. It is not a boring null: it is the first sensitivity-qualified upper limit on the tidal-axis excess after arm-phase control. The bound is reported as the per-sub-region 95% CI on ΔEMdisk> at the E1-calibrated sensitivity floor

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If the result is INCONCLUSIVE> (recovery failure), the page is honest about that. The most likely INCONCLUSIVE branch today is E9 (arm-phase model construction): the Luan & Wang 2025 annulus (45″–110″ = 0.75′–1.83′) overlaps B1/B2 but only partially B3 (r = 1.5–2.0′), so the arm-phase classification is incomplete at the outer radius. The Kuntz+2016 mask covers the full D25 but is Chandra ACIS-S, not XMM EPIC, and the cross-instrument arm-phase transfer is itself an empirical question. If E9 fails, the origin discriminator is absent and I091-G1 fails closed to INCONCLUSIVE — that is the honest answer, not a failure of the page

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If the result is TIDAL-EXCESS>, the symmetric-injection default for tidal interaction signatures in face-on systems is refuted at the most basic level: the arm-phase-controlled contrast shows excess emission along the interaction axis, beyond what the disk's natural azimuthal structure predicts. This constrains tidal-interaction models for hot gas enhancement in galaxy pairs. But>: TIDAL-EXCESS does not> prove the excess is tidally displaced gas — it could be tidally enhanced in-situ disk emission, or an arm-phase misclassification. The arm-phase control is the origin discriminator, but it is necessary, not sufficient. The RF2 firewall requires (a) excess at ≥ 2 of 3 radii surviving arm-phase control, (b) the excess exceeding the simulation-calibrated threshold, and (c) the excess not attributable to NGC 5195 halo contamination (E7 nuisance model

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The honest answer is that the null is not boring — it is a sensitivity-qualified bound on the tidal-axis excess. The page is not asking for compute to discover nobody wanted the result; it is asking for compute to either measure the arm-phase-controlled contrast or bound it. Both are real results

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Geometry — what the new observation looks like on the sky

M51 + NGC 5195 sky geometry on a shared 15 arcmin WCS: DSS2 color (left) and XMM EPIC RGB (right)
M51 + NGC 5195 sky geometry on a shared 15′ WCS (North up, East left). Left> DSS2 color HiPS2FITS (CDS/P/DSS2/color, fov = 0.25°, 1024×1024). Right> XMM EPIC RGB HiPS2FITS (ESDC/P/XMM/EPIC-RGB, same FoV/WCS) — existing archival coverage, not a proposed new pointing. Overlays (both panels):> yellow + = M51 nucleus; cyan + = NGC 5195 nucleus; yellow ellipse = M51 D25 at PA = 163° (semi-axes 5.6′ × 3.45′); cyan circle = NGC 5195 D25 (semi-axis 2.39′); yellow dashed = M51 major axis; yellow dotted = M51 minor axis; white dotted = 15′ PN Full Frame FOV (existing archival coverage). Orange wedges> = I091 Bi> sub-regions along PA = 15.4° (the inter-galaxy axis), centred on the M51 nucleus, NOT the pointing centre — radii r = 0.5–1.0′ / 1.0–1.5′ / 1.5–2.0′ (B1/B2/B3), 30° full wedge (±15° half-width). Green dashed wedge> = Ci> example at B2 radius, placed at the antipodal PA = 195.4° as a geometric placeholder; the actual arm-phase-matched Ci> is selected by the E9 arm-phase model from Luan & Wang 2025 / Kuntz+2016. All Bi> sub-regions are entirely inside M51's projected D25 (max q = 0.060 / 0.135 / 0.240 for B1/B2/B3

The geometry is the R4-verified permanent constraint (cycle-obs9, hermes + terra independent, SHA-256 c5832864…> clean-replay verified). The Bi> sub-regions are 30° wedges (±15° half-width) at galactocentric radii r = 0.5–1.0′ / 1.0–1.5′ / 1.5–2.0′ from the M51 nucleus, along PA ≈ 15.4° (the inter-galaxy axis). The Ci> example shown is at the antipodal PA = 195.4° as a geometric placeholder; the actual arm-phase-matched Ci> is selected by the E9 arm-phase model. The 15′ PN Full Frame FOV (white dotted circle) is the existing archival coverage — all Bi> sub-regions and the Ci> candidates at the same projected radii in non-axis azimuths are within nominal PN FOV geometry

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Audit corrections applied inline> (per the 2026-08-25 first-audit notes): East is plotted to the LEFT (astronomical convention, confirmed by the E← marker); the wedges are centred on the galaxy nucleus (galactocentric), NOT the pointing centre; the Ci> example uses the antipodal PA = 195.4° (not the same PA = 15.4°); the PA→matplotlib conversion is via the WCS itself (world_to_pix), not a manual rotation. The D25 ellipses are drawn at their true PA = 163° for M51 and as a circle for NGC 5195 (semi-axis 2.39′

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Why existing observations are the right starting point

M51 XMM EPIC PN archive coverage by ObsID
M51 XMM EPIC PN archive coverage by ObsID. 15 XMM EPIC ObsIDs, ~575 ks PN scheduled. The M51 archive is substantial: the 0212480801 single observation alone provides ~118 ks of PN exposure (the deepest single ObsID). The mean per-ObsID PN exposure is ~38 ks

M51 has a dedicated XMM EPIC PN archive: 15 ObsIDs, ~575 ks PN scheduled (verified from R0 archive metadata). The Bi> sub-regions at r = 0.5–2.0′ along PA ≈ 15.4° all fall inside the PN Full Frame FOV (15′ radius) for all 15 EPIC science ObsIDs. The arm-phase-matched conjugate Ci> sectors at the same projected radii in non-axis azimuths are also within nominal PN FOV geometry

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Chandra ACIS-S FOV (~8.3′) also covers the sub-regions; the Kuntz+2016 ~755 ks ACIS-S data is the primary resource for arm-phase mask definition (E9). eRASS1 has no coverage (eastern hemisphere, l = 104.85°

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Track = archive> the arm-phase-controlled disk contrast test is archive-first, inherited from I060/I081/I082. A new-obs request is conditional on demonstrating archive insufficiency via the E1 recovery simulation. Whether the arm-phase-controlled azimuthal contrast is measurable at this archival depth is an open empirical question (E1) — no claim that existing data are adequate or inadequate is licensed before E3/E9/E5/E1/E8 execution

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What it costs — and what is still unknown about the cost

Per-sub-region conditional S/N budget (R4 C01 corrected values)
Per-sub-region conditional S/N budget at the I060 B S/N = 10 reference. Blue bars> are the per-sub-region conditional single-sector S/N (R4 C01 corrected: B1 = 2.58, B2 = 3.33, B3 = 3.94 — the idea file's original values 4.47/5.77/6.83 were √3 too high). Orange bars> are the equal-area B-minus-C S/N (the contrast itself: B1 = 1.83, B2 = 2.36, B3 = 2.79). The 2σ detection threshold is shown as a dashed line. The sensitivity trade-off is quantified using corrected values: total solid angle 0.982 arcmin² vs I060 B's 2.945 arcmin² (33.3%).

What we know: the geometry is executable (Bi> sub-regions entirely inside M51 D25, verified to 4 decimals; D25 overlap along axis = 2.6052 arcmin, permanent geometric constraint). The arm-phase control is the origin discriminator that I082 lacked. The S/N budget is quantified using corrected values (R4 C01: √3 lower than the idea file's original

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What we do not know: whether the arm-phase-controlled azimuthal contrast is recoverable at the archival depth. The E1 recovery simulation (response-folded, simulation-calibrated detection probability for ΔEMdisk>(φaxis>, r) vs injected contrast amplitude) is the load-bearing deliverable. Until E1 closes, the exposure requirement is unanchored and the measurement is conditional. The E9 arm-phase model construction (can Luan & Wang 2025 / Kuntz+2016 classify Bi> and Ci> into arm-phase classes at r = 0.5–2.0′?) is the second load-bearing deliverable. If E9 fails, the origin discriminator is absent and I091-G1 fails closed to INCONCLUSIVE

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What it costs (archive-first): zero new XMM time. The cost is the HEAVY R6 work for E3/E9/E5/E1/E7/E8 — the archive-adequacy demonstration, the arm-phase model construction, the contrast-recovery simulation, the sub-region spectral commensurability check, and the joint S/N5195 domain separation. The arm-phase control adds new empirical requirements beyond I082's: E3 (outcome-blind azimuthal D25 survey at each sub-region radius with arm-phase classification of each candidate Ci>), E9 (arm-phase model construction), E5 (same-∇EMdisk> event-level archive extraction from B1/B2/B3 and arm-phase-matched C1/C2/C3 regions), E1 (response-folded contrast-recovery simulation at corrected S/N), E8 (sub-region spectral commensurability

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Gate ledger (D043 — single source of truth

>>> ead> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
GateStatusRole
I091-G1OPEN> D25-geometry-successor fork of I082 with arm-phase-controlled disk azimuthal contrast. RF2 interpretation firewall: TIDAL-EXCESS requires excess surviving arm-phase control + threshold + NGC 5195 halo exclusion; ARM-PHASE-CONSISTENT is a positive outcome (bounds tidal contribution); MIXED/COMPLEX is a positive outcome. E2/E4/E5/E6 inherited from I060/I081/I082 (axis- and sub-region-independent). E3 re-specified for arm-phase-matched control availability. E9 added for arm-phase model construction. E1 re-specified for contrast recovery at corrected S/N. E8 retained for sub-region spectral commensurability. All numerical values EMPIRICAL/needs-data
E2 (inheritedFROZEN> No defensible sourced EMref> in literature; WEAKEN permanently unavailable. Axis- and sub-region-independent
E3 (re-specifiedOPEN — EMPIRICAL> Outcome-blind azimuthal D25 survey at rB1> = 0.75′, rB2> = 1.25′, rB3> = 1.75′ on corrected geometry. Ci> exclusion axis = PA ≈ 15.4° (tidal axis). Candidate Ci> at each radius must have (a) no NGC 5195 overlap, (b) the SAME arm-phase class as Bi> (arm crest / interarm / boundary), (c) no SF complexes. Fail-closed per sub-region: if all three Ci> fail, contrast non-identifiable → INCONCLUSIVE. HEAVY R6
E4 (inheritedFROZEN> N5195(B) nuisance-model form = additive APEC + powerlaw, free norm, no shape borrowing from B, Kuntz+2016 sources excised. Applied per sub-region. Axis- and sub-region-independent
E5 (inheritedFROZEN (scope> Kuntz D25 product disqualified; same-ΔEMdisk> archive test requires frozen B1/B2/B3 + operative estimand. Exact polygon EMPIRICAL/R6
E6 (inheritedFROZEN — NEEDS-DATA> R3 literature path closed (9 ADS query families exhausted). WEAKEN unavailable. Axis- and sub-region-independent
E1 (re-specifiedOPEN — EMPIRICAL> Contrast-recovery simulation at corrected S/N (B1 = 2.58, B2 = 3.33, B3 = 3.94 at I060 B S/N = 10 per R4 C01; equal-area B-minus-C: 1.83 / 2.36 / 2.79). EM = APEC norm → EM via T74 distance-scaled volume (d ≈ 8.6 Mpc). Recovery = simulation-calibrated detection probability for the azimuthal contrast ΔEMdisk>(φaxis>, r) vs injected contrast amplitude. Coverage = calibrated 95% CI. Adequacy = ≥ 50% recovery of the contrast sign at frozen scale using actual clean exposure. Filter-specific response (0212480801 MEDIUM vs THIN1). HEAVY R6
E7 (re-specifiedOPEN — EMPIRICAL> Joint S (signal sub-regions B1/B2/B3) and N5195(B) domain separation on corrected geometry. N5195(B) is outside D25 for all sub-regions (B3 at 2.66′ from NGC 5195, outside D25 radius 2.39′), so the N5195 halo contribution is a nuisance. Response/PSF/vignetting covariance per sub-region. HEAVY R6
E8 (retainedOPEN — EMPIRICAL> Sub-region spectral commensurability: B1/B2/B3 and C1/C2/C3 must be response-folded on a common energy/response basis. The sub-regions span different vignetting/PSF/effective-area regimes; per-sub-region ARF/RMF differences must be quantified and either corrected or shown to be sub-dominant to the contrast signal. HEAVY R6
E9 (newOPEN — EMPIRICAL> Arm-phase model construction: can the Luan & Wang 2025 18-region log-spiral phase decomposition (T254) and/or the Kuntz+2016 Chandra ACIS-S arm/interarm mask (T143) be used to classify Bi> and Ci> into arm-phase classes at r = 0.5–2.0′? The Luan & Wang annulus (45″–110″ = 0.75′–1.83′) overlaps B1/B2 but only partially B3 (r = 1.5–2.0′). The Kuntz+2016 mask covers the full D25. The arm-phase model must be frozen before E3 control selection. If the arm-phase model cannot be constructed, the origin discriminator is absent and I091-G1 fails to INCONCLUSIVE. HEAVY R3/R6

What I am and am not claiming

I am claiming> the science question is real (tidal interactions in face-on galaxy pairs are a load-bearing belief in subgrid-feedback recipes and the arm-phase-controlled contrast is the missing origin discriminator); the geometry is constrained (Bi> sub-regions entirely inside M51 D25, D25 overlap along axis = 2.6052 arcmin, permanent geometric constraint); the arm-phase control is the origin discriminator that I082 lacked; the S/N budget is quantified using corrected values (R4 C01: B1 = 2.58, B2 = 3.33, B3 = 3.94 at I060 B S/N = 10); and the E9 arm-phase model construction is the load-bearing empirical deliverable

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I am not claiming> that

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  • A TIDAL-EXCESS result would prove> the excess is tidally displaced gas — it could be tidally enhanced in-situ disk emission, or an arm-phase misclassification. The arm-phase control is necessary, not sufficient (RF2 firewall
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  • An ARM-PHASE-CONSISTENT result would prove> there is no tidal contribution — it bounds the observable contribution above the sensitivity floor
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  • One galaxy can "validate" a population-level or cosmological prescription — I091 constrains this galaxy, this epoch, this projected scale, this phase, at this precision
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  • The arm-phase control is tautologically circular — the R4 third-pass REFRAME (arm-phase = EM class per Luan & Wang 2025, so the control matches the same variable that the contrast measures) is preserved as a NOTE in the R5 adjudication; the arm-phase control is a model-residual characterization, not an origin discrimination in the strict causal sense. The I091 estimand is the EM residual after subtracting an arm-phase EM model from the tidal-axis direction
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  • The 15′ PN Full Frame FOV circle is response/extraction feasibility — it is nominal circular containment, not detector footprint, CCD gaps, vignetting, usable exposure, or off-axis response. Those are E1/E8 EMPIRICAL
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  • The existing archive is adequate or inadequate for the contrast — that is the E1 recovery simulation's job
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Why this page exists

I091 is currently parked_hold> per the cycle-obs9 R5 adjudication (cycles/cycle-obs9/r5_adjudication_i091.md>, 2026-08-11). The hold is routing, not acceptance of an R4 scientific verdict: I097 is the already-executed active redesign successor and routes to R2 new_idea>. The original I091 design stays recoverable as a fully recorded lineage node. The page is the artifact that makes the I091 judgement possible — what the question is, why anyone should care, what the measurement would show, and what it would look like if the answer came out the other way

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HEAVY is paused (PI, 2026-08-23). An idea does not reach compute by asking for it — it reaches compute by being written up as a page the PI reads and approves. This page is that artifact for I091

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Provenance

  • Idea file: shared/ideas/I091_m51-disk-azimuthal-tidal-axis-contrast-fork.md
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  • R2 Admission: cycles/cycle-obs9/r2_admission_i091_fork.md> (cycle-obs9, hermes, 2026-08-09
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  • R5 Adjudication: cycles/cycle-obs9/r5_adjudication_i091.md> (cycle-obs9, 2026-08-11, status: audited-parent-hold
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  • R4 Geometry anchor: cycles/cycle-obs9/materials/R4_I082_terra_anchor_checks_v2.json> (SHA-256 c5832864471166b704e520eb3be6cd7dc62235a6443d5c2a7db9cd9d417ced5b>, clean-replay verified
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  • R4 Second-anchor (LandW coverage): cycles/cycle-obs9/materials/R4_I091_hermes_second_anchor.json> (SHA-256 e7d838a928601fe2b541774012d1fda9140f7456039f62aca79796376c861eeb>, clean-replay verified
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  • Luan & Wang 2025 source card: shared/sources/papers/Luan+Wang_2025.md
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  • SIMBAD coordinates (M51 + NGC 5195): cycles/cycle-obs9/materials/R4_I012_simbad_coordinates_20260807.json> (SHA-256 069c857accad0297899e508263b49ef1e007107e9757c3357806d153254e08c1
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  • Figure provenance: fig/fig1_provenance.json> (geometry, S/N, WCS, all numerical values
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  • HiPS2FITS source FITS: CDS/P/DSS2/color> and ESDC/P/XMM/EPIC-RGB>, fetched 2026-08-25 from https://alasky.cds.unistra.fr/hips-image-services/hips2fits> (fov = 0.25° = 15 arcmin, 1024×1024, ICRS
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Geometry replay command> (used to compute D25 overlap and sub-region max-q):

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python3 cycles/cycle-obs9/r4_i082_terra_anchor_checks.py --output /tmp/r5_i091_i082_anchor_replay_20260811.json
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Result: M51→NGC 5195 PA = 15.374°; all I082 sub-regions inside projected M51 D25 (max-q B1 = 0.060, B2 = 0.135, B3 = 0.240); D25 overlap along axis = 2.605 arcmin. Conditional single-sector S/N at I060 B S/N = 10: B1 = 2.58, B2 = 3.33, B3 = 3.94 (R4 C01 corrected
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