Pantheon+ supernovae corrected for progenitor age indicate the universe is decelerating

Abstract

We examine the impact of progenitor age-dependent luminosity evolution of Type Ia supernovae on a cosmographic measurement of the deceleration parameter $q_0$. Our recent redshift tomographic analysis showed that locally $q_0$ has a strong dipole anisotropy aligned approximately with the bulk flow, and only a small monopole component remains at distances exceeding a few hundred Mpc. Applying redshift-dependent corrections for progenitor age to the Pantheon+ catalogue, we find that this shifts the monopole component of $q_0$ to positive values (i.e. deceleration), while leaving the local dipole component essentially unchanged.

Comments: 5 pages, 4 figures, 2 tables; to appear as a Letter in Monthly Notices of the Royal Astronomical Society