On the use of the local prior on the absolute magnitude of Type Ia supernovae in cosmological inference
Abstract
A darkenergy, which behaves as the cosmological constant until a sudden phantom transition at very low redshift (z < 0.1), seems to solve the >4σ disagreement between the local and highredshift determinations of the Hubble constant, while maintaining the phenomenological success of the Λ cold dark matter model with respect to the other observables. Here, we show that such a hockeystick dark energy cannot solve the H_{0} crisis. The basic reason is that the supernova absolute magnitude M_{B} that is used to derive the local H_{0} constraint is not compatible with the M_{B} that is necessary to fit supernova, baryon acoustic oscillation, and cosmic microwave background data, and this disagreement is not solved by a sudden phantom transition at very low redshift. We make use of this example to show why it is preferable to adopt in the statistical analyses the prior on M_{B} as an alternative to the prior on H_{0}. The three reasons are: (i) one avoids potential double counting of lowredshift supernovae, (ii) one avoids assuming the validity of cosmography, in particular, fixing the deceleration parameter to the standard model value q_{0} = 0.55, (iii) one includes in the analysis the fact that M_{B} is constrained by local calibration, an information which would otherwise be neglected in the analysis, biasing both model selection and parameter constraints. We provide the priors on M_{B} relative to the recent Pantheon and DESSN3YR supernova catalogs. We also provide a Gaussian joint prior on H_{0} and q_{0} that generalizes the prior on H_{0} by Supernova H0 for the Equation of State.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 2021
 DOI:
 10.1093/mnras/stab1200
 arXiv:
 arXiv:2101.08641
 Bibcode:
 2021MNRAS.504.5164C
 Keywords:

 cosmological parameters;
 dark energy;
 cosmology: observations;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 9 pages, 6 figures, 3 tables. Title changed to better describe the scope, expanded analysis and discussion, v3 reflects version accepted for publication in MNRAS