“Supernovae Ia Twins” in the Hubble Flow, and the Determination of H 0

Abstract We have applied our approach of using “supernovae (SNe) Ia twins” in the Hubble flow to obtain distances to SNe Ia at z > 0.015 and derive H 0 . Our results, taking a single step between the low- z domain and the Hubble flow, validate the three-rung classical method. We find, however, that the full compilation of distances, both in Pantheon+ and in the Carnegie-Chicago Hubble Program (CCHP), contains some inaccurate values in the colors due to an underestimate of reddening by dust, or due to the adoption of not well-defined light curve declines. This produces odd individual values for H 0 from single SNe Ia. On average, those erroneous estimates do not affect the mean value of H 0 , which is characterized by the bulk of well-modeled SNe Ia. Our sample of carefully addressed SNe Ia in the Hubble flow contains a dozen SNe, for which the distances are determined with high accuracy. Three of these SNe Ia are of the broad-line subtype and can be compared with SN 1989B in M66, a host galaxy with a unique convergence of the Cepheid distance determination and the tip of the red giant branch stars determination by the CCHP group. There is also a very good agreement on the distances to NGC 7250 and NGC 5643 between those derived with Cepheids by SH0ES and those derived with the use of J -asymptotic giant branch (JAGB) stars by the CCHP, which makes them very good anchors. The sample of 12 SNe Ia gives a value of H 0 = 72.56 ± 1.54 (stat) ± 1.33 (sys) km s −1 Mpc −1 , when anchored in Cepheids, and of H 0 = 72.20 ± 1.53 (stat) ± 1.33 (sys) km s −1 Mpc −1 , when anchored in JAGB stars by the CCHP. We take a mean of the two values of H 0 as derived by the Cepheids and by JAGB stars (from the CCHP) and obtain H 0 = 72.38 ± 1.54 (stat) ± 1.33 (sys) km s −1 Mpc −1 . Our findings confirm that the Hubble tension is real.