Hubble Constant and Mass Determination of Centaurus A & M83 from TRGB Distances

An independent determination of the Hubble constant is crucial given the persistent tension between early- and late-Universe measurements. In this study, we analyze 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 the Hubble constant ($H_0$). By examining the motions of these galaxies relative to the system's barycenter, we apply 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 $(7.3 \pm 2.0) \times 10^{12}\,M_{\odot}$ and a Hubble flow-based mass of $(2.6 \pm 1.4) \times 10^{12}\,M_{\odot}$. Modeling the cold Hubble flow around the group center of mass yields a corresponding Hubble constant of $(64.0 \pm 4.6)\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$. These results offer an independent, dynamically motivated constraint on the local value of $H_0$, explicitly accounting for the impact of peculiar velocities in the nearby Universe. We also discuss the $\sim 2σ$ tension between the virial and Hubble flow-based mass estimates, which likely arises from the proximity of M83 to the velocity surface, breaking the assumptions of the Hubble flow model. While the Hubble flow fit emphasizes galaxies that follow smooth expansion on the lower branch of the velocity-distance relation, the virial mass estimate is in good agreement with the group mass derived from the $K$-band luminosity of its brightest members and from projected mass methods.

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