Anisotropy of the Universe via the Pantheon supernovae sample revisited

Abstract

We employ the hemisphere comparison (HC) method and the dipole fitting (DF) method to investigate the cosmic anisotropy in the recently released Pantheon sample of type Ia supernovae (SNe Ia) and five combinations among Pantheon. For the HC method, we find the maximum anisotropy level in the full Pantheon sample is AL max = 0.361 ± 0.070 and corresponding direction (l, b) = (123.05A robust check shows the statistical significance of maximum anisotropy level is about 2.1σ. We also find that the Low-z and SNLS subsamples have decisive impact on the overall anisotropy while other three subsamples have little impact. Moreover, the anisotropy level map significantly rely on the inhomogeneous distribution of SNe Ia in the sky. For the DF method, we find the dipole anisotropy in the Pantheon sample is very weak. The dipole magnitude is constrained to be less than 1.16 × 10 −3 at 95% confidence level. However, the dipole direction is well inferred by MCMC method and it points towards (l, b) = (306.00 •+82.95 • −125.01 • , −34.20 •+16.82 • −54.93 • ). This direction is very close to the axial direction to the plane of SDSS subsample. It may imply that SDSS subsample is the decisive part to the dipole anisotropy in the full Pantheon sample. All these facts imply that the cosmic anisotropy found in Pantheon sample significantly rely on the inhomogeneous distribution of SNe Ia in the sky. More homogeneous distribution of SNe Ia is necessary to search for a more convincing cosmic anisotropy.

Exploring the evidence for a large local void with supernovae Ia data

“…Our result for the level of local anisotropy in Pantheon SN Ia is consistent with previous works that find null evidence against assumption of the isotropy (Andrade et al 2018;Zhao et al 2019b), although less stringent compared to global anisotropy constraint found by Soltis et al (2019). Analogously to eq.…”

The Hubble Tension, the M Crisis of Late Time H(z) Deformation Models and the Reconstruction of Quintessence Lagrangians

“…The constraints obtained using the Pantheon dataset are in agreement with corresponding previous studies [5,42,68].…”

Constraining the anisotropy of the Universe with the Pantheon supernovae sample *

“…The dipole directions in four cosmological models by using the Pantheon sample, and the dipole directions derived from the Union2 sample[39], Union2.1 sample[44] and JLA sample[50]. The star marks the axial direction to the plane of SDSS subsample[65]. The uncertainties of dipole directions could be found inTable 1. xxxxxx-9 towards (l, b) = (298.81 •+84.18 • −118.71 • , −19.80 •+14.07 • −63.25 • ), which is very close to the dipole direction in the dipole-modulated ΛCDM model.…”