The Local Perspective on the Hubble Tension: Local Structure Does Not Impact Measurement of the Hubble Constant

TL;DR

This work tests whether local cosmic variance in the form of a large nearby void could bias SN Ia determinations of the Hubble constant, contributing to the Hubble tension. By assembling the largest spectroscopic SN Ia sample to date (1295 SNe, $0.01<z<2.26$) from Pantheon, Foundation, and CSP, and modeling local inhomogeneity with a LTB void, the authors quantify any redshift-dependent shift in the Hubble intercept. They find no evidence that local voids of the proposed amplitudes affect $H_0$ within the SN-based distance ladder, with an empirical precision of $\sigma_{H_0}=0.60\%$ and a cosmic variance expectation of $0.42\%$, confirming that local structure does not resolve the Hubble tension. A 5$\sigma$ bound constrains local density contrasts on $>69\ \mathrm{Mpc}\,h^{-1}$ scales to $|\delta|<0.27$, reinforcing that local structure does not impede achieving ~1% precision in $H_0$ from SN data.

Abstract

We use the largest sample to date of spectroscopic SN Ia distances and redshifts to look for evidence in the Hubble diagram of large scale outflows caused by local voids suggested to exist at z<0.15. Our sample combines data from the Pantheon sample with the Foundation survey and the most recent release of lightcurves from the Carnegie Supernova Project to create a sample of 1295 SNe over a redshift range of 0.01<z<2.26. We make use of an inhomogeneous and isotropic Lemaitre-Tolman-Bondi metric to model a void in the SN Ia distance-redshift relation. We conclude that the SN luminosity distance-redshift relation is inconsistent at the 4-5 sigma confidence level with large local underdensities (|delta| > 20%, where the density contrast delta = Delta rho /rho) proposed in some galaxy count studies, and find no evidence of a change in the Hubble constant corresponding to a void with a sharp edge in the redshift range 0.023<z<0.15. With empirical precision of sigma_H_0 = 0.60%, we conclude that the distance ladder measurement is not affected by local density contrasts, in agreement with cosmic variance of sigma_H_0 = 0.42% predicted from simulations of large-scale structure. Given that uncertainty in the distance ladder value is sigma_H_0=2.2%, this does not affect the Hubble tension. We derive a 5 sigma constraint on local density contrasts on scales larger than 69 megaparsec h^-1 of delta < 27%. The presence of local structure does not appear to impede the possibility of measuring the Hubble constant to 1% precision.

Figures (2)

• Figure 1: Upper panel: Density contrast $\delta (r)$ of the KBC model as a function of radial coordinate $r$. Lower panel: Predicted expansion rate of the same KBC model as a function of $z$ relative to expansion rate of a $\Lambda$CDM cosmology with $H_0=73.2km\per s\per M\parsec,\Omega_M=0.3$. The expansion rate $H(z)$ is defined as $H^{KBC}(z)=\dot{R}(r(z),t(z))/R(r(z),t(z))$ for the KBC model and $H^{\Lambda CDM}(z)=\dot{a}(z)/a(z)$ for the $\Lambda$CDM model.
• Figure 2: Magnitude-redshift Hubble diagram. Intercept of the Hubble diagram determines the Hubble constant. Red lines show the edges of redshift range for primary fit, $0.01<z<0.50$