2021MNRAS.500.3728S

The discrepancy between estimates of the Hubble constant (H₀) measured from local (z <= 0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (v_pec) of standard candle distance indicators can systematically affect local H₀ measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z < 0.05 underdensity in the SGC-6dFGS region of 27 ± 2 per cent. However, no strong evidence for a 'Local Void' pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δph_±, which we introduce as a proxy for v_pec that quantifies density gradients along a supernova (SN) line of sight. Δph_± is found to correlate with local H₀ estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02 < z < 0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H₀ estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H₀ with Δph_±, we can correct for the effects of density structure on local H₀ estimates, even in the presence of biased v_pec. However, the difference in the inferred H₀ estimate with and without the peculiar velocity correction is limited to < 0.1 per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H₀ estimates.