A cosmological underdensity does not solve the Hubble tension

• Published in: Journal of cosmology and astroparticle physics Vol. 2022; no. 7; pp. 3 - 27
• Main Authors: Castello, Sveva, Högås, Marcus, Mörtsell, Edvard
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.07.2022
• Subjects: baryon acoustic oscillations; Calibration; cosmic web; cosmological parameters from CMBR; Cosmology; Data points; Datasets; Density; Parameterization; Red shift; supernova type Ia - standard candles; Supernovae; Tension
• ISSN: 1475-7516; 1475-7516
• DOI: 10.1088/1475-7516/2022/07/003

Abstract A potential solution to the Hubble tension is the hypothesis that the Milky Way is located near the center of a matter underdensity. We model this scenario through the Lemaître-Tolman-Bondi formalism with the inclusion of a cosmological constant (ΛLTB) and consider a generalized Gaussian parametrization for the matter density profile. We constrain the underdensity and the background cosmology with a combination of data sets: the Pantheon Sample of type Ia supernovae (both the full catalogue and a redshift-binned version of it), a collection of baryon acoustic oscillations data points and the distance priors extracted from the latest Planck data release. The analysis with the binned supernovae suggests a preference for a -13 % density drop with a size of approximately 300 Mpc, interestingly matching the prediction for the so-called KBC void already identified on the basis of independent analyses using galaxy distributions. The constraints obtained with the full Pantheon Sample are instead compatible with a homogeneous cosmology and we interpret this radically different result as a cautionary tale about the potential bias introduced by employing a binned supernova data set. We quantify the level of improvement on the Hubble tension by analyzing the constraints on the B-band absolute magnitude of the supernovae, which provides the calibration for the local measurements of H 0 . Since no significant difference is observed with respect to an analogous fit performed with a standard ΛCDM cosmology, we conclude that the potential presence of a local underdensity does not resolve the tension and does not significantly degrade current supernova constraints on H 0 .