Distance modulus
We use each CF4 group's selected representative position, published combined modulus and quoted marginal error. The approximate response is δμ ≈ −(5/ln 10)δu/(H₀D), conditional on H₀ = 70 km/s/Mpc.
GREAT ATTRACTOR / CONDITIONAL DESIGN TEST
Can we tell a local pull from a wider flow?
Real survey positions. Explicit competing motions. A sensitivity forecast, not a detection.
The question is whether current independent distance measurements can separate a localized inward-flow pattern near Norma from external bulk motion, shear and a global distance-scale shift.
Read this number correctly. The 98 km/s value below is a conditional one-sigma error forecast for one assumed template. We have not fitted an observed Great Attractor amplitude, velocity field or mass.
CF4 records in 40–100 Mpc shell8,861Measured distance moduli and positions
One per published group reference6,777Primary calculation; still correlated across groups
Inside 20° Norma cone8649 near side · 37 far side
Fiducial conditional σA98.14km/s · model assumptions below
01 / WHAT THE REAL FOOTPRINT COULD RESOLVE
A hypothesis has a measurable shape.
Each curve changes the assumed spatial width of the localized flow. The height is the expected one-sigma amplitude error after removing the best-matching bulk, shear and scale signal.
INSPECT A PRECOMPUTED HYPOTHESIS
Change the assumed shape.
Select the centre and width of the illustrative inward-flow template. The readout comes from the checked-in calculation; changing it does not refit galaxy observations.
Conditional 1σ amplitude error98.14 km/s
93.3% of the raw template information remains after projection onto nuisance motions.
Loading the reproducible scenario grid…
02 / WHAT WENT INTO THE NUMBER
A forecast with visible assumptions.
Bulk, shear, scale
A three-component uniform flow, five-component trace-free shear and one unrestricted global modulus offset are projected out before calculating information on the local template.
Optimistic by design
Quoted per-record σμ is combined with an assumed 250 km/s independent small-scale scatter. Inter-group calibration and spatial covariance, selection and template errors are absent; the resulting sensitivity may be too optimistic.
A CHECK AGAINST FALSE PRECISION
Groups and methods matter.
Treating all 8,861 records as independent gives 85.65 km/s; one representative per published group gives 98.14 km/s. Assumed small-scale scatter of 150–400 km/s moves that result from 92.89 to 107.53 km/s. Excluding Tully–Fisher-associated representatives leaves 1,730 and weakens it to 168.20 km/s. Method masks indicate presence, not independent method-specific distances. These are conditional coverage tests.
WHAT WOULD BE REQUIRED NEXT
Fit observables, then test predictions.
Use a density-derived template, coherent frame and selection-aware forward likelihood. Propagate shared anchors and spatial covariance, inject competing fields into mocks, and evaluate predictions on held-out group and method blocks. A Planck CMB image cannot substitute for those measurements.
REPRODUCE AND CHALLENGE THE RESULT
Open inputs. Open calculation. Open limits.
The complete CF4 table and provenance are available in the catalog explorer. The linked methods note spells out the field, derivatives, cuts and limitations; the JSON contains every precomputed scenario.
Data: Tully et al., Cosmicflows-4. Related approaches: CF4 forward modelling and 2MRS–CF4 comparison. This project does not claim the flow-decomposition method is new.