Bulk Flow Motion Detection in the Local Universe with Pantheon+ Type Ia Supernovae

Abstract

The bulk flow in the Local Universe is a collective phenomenon due to the peculiar motions of matter structures, which, instead of moving in random directions, appears to follow an approximate dipole velocity flow. We apply a directional analysis to investigate, through the Hubble-Lemaître diagram, the angular dependence of the Hubble constant H 0 of a sample of Type Ia supernovae from the Pantheon+ catalog in the Local Universe (0.015 ≤ z ≤ 0.06). We perform a directional analysis that reveals a statistically significant dipole variation of H 0, at more than 99.9% confidence level, showing that matter structures follow a dipole bulk flow motion toward (l, b) = (326.°1 ± 11.°2, 27.°8 ± 11.°2), close to the Shapley supercluster (l Shapley, b Shapley) = (311.°5, 32.°3), with velocity 132.14 ± 109.3 km s−1 at the effective distance 102.83 ± 10.2 Mpc. Interestingly, the antipodal direction of this dipole points close to the Dipole Repeller structure. Our analyses confirm that the gravitational dipole system Shapley-Dipole Repeller explains well the observed bulk flow velocity field in the Local Universe. Furthermore, we performed robustness tests that support our results. Additionally, our approach provides a measurement of the Hubble constant H 0 = 70.39 ± 1.4 km s−1 Mpc−1, at the effective distance 102.8 Mpc, z ≃ 0.025.