Local few-hundred-megaparsec Hubble–Lemaître analysis with minimal model dependence

Local few-hundred-megaparsec Hubble–Lemaˆıtre analysis with minimal model dependence Boud Roukema Institute of Astronomy NCU DOI:10.5281/zenodo.17725355 17 Sep 2025 Rubin–LSST@Europe7 @Pozna´n Overview ▶context: FLRW interpretation of data is over restrictive ▶aim: infer cosmological line element @few 100 Mpc with many fewer assumptions ▶method: –theory: “quiet universe” assumption – Heinesen & Macpherson 2022 ArXiv:2111.14423 –data: Rubin–LSST + spectro followup 4MOST + DESI Assumptions – details ▶Lorentzian spacetime –∀xtangent @x= Minkowski spacetime ▶geometrical optics ▶Etherington’s reciprocity theorem — dL= (1 + z)2dA ▶congruence of light paths from emitters to observer ▶negligible caustics ▶convergence of dLin z ⇒roughly speaking, not too far from FLRW for z≪1 Cosmographic parameters ▶observational aim: determine Ho,Qo,Ro,Jo from SNe Ia ▶dL=d(1) Lz+d(2) Lz2+d(3) Lz3+O(z4) where d(1) L=f(Ho), d(2) L=f(Ho,Qo), d(3) L=f(Ho,Qo,Ro,Jo) –variation over sky – dipoles, quadrupoles Cosmographic predictions (HM2022) ▶Hodipole = 0 ▶Qodipole: 1 qµ∝Dµθ∝Dµρ– aligned with matter spatial-gradient •(Ro– fully dependent on Ho,Qo,Jo) ▶Jodipole: 1 jµ∝Dµθ∝Dµρ– aligned with Qo dipole and matter spatial-gradient Analysis aim ▶find best fit monopoles, dipoles and quadrupoles of Ho,Qo,Ro,Join dL(z) relation ▶cf Dhawan+2022 ▶Pantheon + JLA ▶no significant dipole, quadrupole detected in Ho, Qoin CMB frame after accounting for peculiar velocities Dhawan+2022: deceleration moments (See Fig. 4a (non-free licence) of Dhawan+2022) Dhawan+2022 – JLA Qodipole qdvs monopole qm Heliocen CMB HD = pec vel corr. Dhawan+2022: deceleration moments (See Fig. 4b (non-free licence) of Dhawan+2022) Dhawan+2022 – Pantheon Qodipole qdvs monopole qm Heliocen CMB HD = pec vel corr. Caveats ▶how much will non-uniform, non-4πsky coverage bias the results? ▶can the full selection functions (sky →Rubin →redshifts) be modelled accurately?