Isotropy properties of the absolute luminosity magnitudes of SnIa in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Pantheon</mml:mi><mml:mo>+</mml:mo></mml:mrow></mml:math> and SH0ES samples
Leandros Perivolaropoulos
Abstract
We use the hemisphere comparison method to test the isotropy of the SnIa absolute magnitudes of the $\mathrm{Pantheon}+$ and SH0ES samples in various redshift/distance bins. We compare the identified levels of anisotropy in each bin with Monte Carlo simulations of corresponding isotropized data to estimate the frequency of such levels of anisotropy in the context of an underlying isotropic cosmological model. We find that the identified levels of anisotropy in all bins are consistent with the Monte Carlo isotropic simulated samples. However, in the real samples for both the $\mathrm{Pantheon}+$ and the SH0ES cases, we find sharp changes of the level of anisotropy occurring at distances less than 40 Mpc. For the $\mathrm{Pantheon}+$ sample, we find that the redshift bin [0.005, 0.01] is significantly more anisotropic than the other five redshift bins considered. For the SH0ES sample, we find a sharp drop of the anisotropy level at distances larger than about 30 Mpc. These anisotropy transitions are relatively rare in the Monte Carlo isotropic simulated data and occur in 2% of the SH0ES simulated data and at about 7% of the $\mathrm{Pantheon}+$ isotropic simulated samples. This effect is consistent with the experience of an off-center observer in a 30 Mpc bubble of distinct physics or systematics.