Local determination of the Hubble constant and the deceleration parameter

The determination of the Hubble constant H-0 from the cosmic microwave background by the Planck Collaboration (N. Aghanim et al., arXiv:1807.06209) is in tension at 4.2 sigma with respect to the local determination of H-0 by the SH0ES collaboration [M. J. Reid et al., Astrophys. J. Lett. 886, L27 (2019)]. Here we improve upon the local determination, which fixes the deceleration parameter to the standard Lambda CDM model value of q(0) = -0.55, that is, uses information from observations beyond the local universe. First, we derive the effective calibration prior on the absolute magnitude M-B of type Ia supernovae, which can be used in cosmological analyses in order to avoid the double counting of low-redshift supernovae. We find M-B = -19.2334 +/- 0.0404 mag. Then we use the above M-B prior in order to obtain a determination of the local H-0 which uses only local observations and assumes only the cosmological principle, that is, large-scale homogeneity and isotropy. This is achieved by adopting an uninformative flat prior for q(0) in the cosmographic expansion of the luminosity distance. We use the latest Pantheon sample and find H-0 = 75.35 +/- 1.68 km s(-1) Mpc(-1), which features a 2.2% uncertainty, close to the 1.9% error obtained by the SH0ES Collaboration. Our determination is at the higher tension of 4.5 sigma with the latest results from the Planck Collaboration that assume the Lambda CDM model. Furthermore, we also constrain the deceleration parameter to q(0) = -1.08 +/- 0.29, which disagrees with the Planck Collaboration at the 1.9 sigma level. These estimations only use supernovae in the redshift range 0.023 <= z <= 0.15.