2022A&A...662A..57M

The nearby elliptical galaxy Centaurus A (Cen A) is surrounded by a flattened system of dwarf satellite galaxies with coherent motions. Using a novel Bayesian approach, we measured the mean rotation velocity v_rot and velocity dispersion σ_int of the satellite system. We found v_rot/σ_int ≃ 0.7, indicating that the satellite system has non-negligible rotational support. Using Jeans' equations, we measured a circular velocity of 258 km s^–1 and a dynamical mass of 1.2 x 10¹³ M_☉ within 800 kpc. In a Λ cold dark matter cosmological context, we found that the Cen A group has a baryon fraction M_b/M₂₀₀ ≃ 0.035 and is missing ∼77% of the cosmologically available baryons. Consequently, Cen A should have a hot intergalactic medium with a mass of ∼8 x 10¹¹ M_☉, which is more than ∼20 times larger than current X-ray estimates. Intriguingly, the whole Cen A group lies on the baryonic Tully-Fisher relation defined by individual rotationally supported galaxies, as expected in Milgromian dynamics (MOND) with no need of missing baryons.