%0 Generic %1 giani2023effective %A Giani, L. %A Howlett, C. %A Said, K. %A Davis, T. %A Vagnozzi, S. %D 2023 %K astronomy cosmology hubble_constant hubble_tension laniakea %T An effective description of Laniakea and its backreaction: Impact on Cosmology and the local determination of the Hubble constant %U http://arxiv.org/abs/2311.00215 %X We propose an effective model to describe the backreaction on cosmological observables induced by Laniakea, the gravitational supercluster hosting the Milky Way, which was defined using peculiar velocity data from Cosmicflows-4 (CF4). The structure is well described by an ellipsoidal shape exhibiting triaxial expansion, reasonably approximated by a constant expansion rate along the principal axes. Our best fits suggest that the ellipsoid, after subtracting the background expansion, contracts along the two smaller axes and expands along the longest one, predicting an average expansion of $-1.1 ~km/s/Mpc$. The different expansion rates within the region, relative to the mean cosmological expansion, induce line-of-sight-dependent corrections in the computation of luminosity distances. We apply these corrections to two low-redshift datasets: the Pantheon+ catalog of type Ia Supernovae (SN~Ia), and 63 measurements of Surface Brightness Fluctuations (SBF) of early-type massive galaxies from the MASSIVE survey. We find corrections on the distances of order $2-3\%$, resulting in a shift in the inferred best-fit values of the Hubble constant $H_0$ of order $\Delta H_0^SN~Ia0.5 ~km/s/Mpc$ and $\Delta H_0^SBF1.1 ~km/s/Mpc$, seemingly worsening the Hubble tension.

@misc{giani2023effective, abstract = {We propose an effective model to describe the backreaction on cosmological observables induced by Laniakea, the gravitational supercluster hosting the Milky Way, which was defined using peculiar velocity data from Cosmicflows-4 (CF4). The structure is well described by an ellipsoidal shape exhibiting triaxial expansion, reasonably approximated by a constant expansion rate along the principal axes. Our best fits suggest that the ellipsoid, after subtracting the background expansion, contracts along the two smaller axes and expands along the longest one, predicting an average expansion of $\sim -1.1 ~\rm{km}/\rm{s}/\rm{Mpc}$. The different expansion rates within the region, relative to the mean cosmological expansion, induce line-of-sight-dependent corrections in the computation of luminosity distances. We apply these corrections to two low-redshift datasets: the Pantheon+ catalog of type Ia Supernovae (SN~Ia), and 63 measurements of Surface Brightness Fluctuations (SBF) of early-type massive galaxies from the MASSIVE survey. We find corrections on the distances of order $\sim 2-3\%$, resulting in a shift in the inferred best-fit values of the Hubble constant $H_0$ of order $\Delta H_0^{\rm{SN~Ia}}\approx 0.5 ~\rm{km}/\rm{s}/\rm{Mpc}$ and $\Delta H_0^{\rm{SBF}}\approx 1.1 ~\rm{km}/\rm{s}/\rm{Mpc}$, seemingly worsening the Hubble tension.}, added-at = {2023-11-22T15:33:48.000+0100}, author = {Giani, L. and Howlett, C. and Said, K. and Davis, T. and Vagnozzi, S.}, biburl = {https://www.bibsonomy.org/bibtex/2593d012f1e06d37a6a036d3559bef38b/tabularii}, description = {[2311.00215] An effective description of Laniakea and its backreaction: Impact on Cosmology and the local determination of the Hubble constant}, interhash = {0fe142d5811af70caca130304645edcc}, intrahash = {593d012f1e06d37a6a036d3559bef38b}, keywords = {astronomy cosmology hubble_constant hubble_tension laniakea}, note = {cite arxiv:2311.00215Comment: Sixteen pages + references, 12 figures, 1 appendix. Comments are welcome!}, timestamp = {2023-11-22T15:33:48.000+0100}, title = {An effective description of Laniakea and its backreaction: Impact on Cosmology and the local determination of the Hubble constant}, url = {http://arxiv.org/abs/2311.00215}, year = 2023 }