Hubble-constant and -mass determination of Centaurus A and M83 from tip-of-red-giant-branch distances

An independent determination of the Hubble constant is crucial in light of the persistent tension between early- and late-Universe measurements. In this study, we analysed the dynamics of the Centaurus A (CenA) and M83 galaxies, along with their associated dwarf companions identified via tip-of-the-red-giant-branch (TRGB) distance measurements, to constrain both the group mass and the local value of H0. By examining the motions of these galaxies relatively to the system’s barycentre, we applied both the minor and major infall models, which provide bounds on the true radial-velocity dispersion. From the overlap of these approaches, we obtain a virial mass estimate of (7.3 ± 2.0)×1012 M⊙ and a Hubble-flow-based mass of (2.6 ± 1.4)×1012 M⊙. Modeling the cold Hubble flow around the group centre of mass, we derive a corresponding value of the Hubble constant as (64.0 ± 4.6) km s−1 Mpc−1. These results offer an independent, dynamically motivated constraint on the local value of H0, explicitly accounting for the impact of peculiar velocities in the nearby Universe. We also discuss the ∼2σ tension between the virial and Hubble-flow-based mass estimates, which likely arises from the fact that M83 is close to the velocity surface and goes against the Hubble-flow-model assumptions. While the Hubble-flow fit emphasises galaxies that follow smooth expansion on the lower branch of the velocity-distance relation, the virial mass estimate is found to be in good agreement with the group mass derived from the K-band luminosity of its brightest members and the projected mass methods.