The Cen A galaxy group: Dynamical mass and missing baryons

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 nu(rot) and velocity dispersion sigma(int) of the satellite system. We found nu(rot)/sigma(int) similar or equal to 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 10(13 )M(circle dot) within 800 kpc. In a Lambda cold dark matter cosmological context, we found that the Cen A group has a baryon fraction M-b/M-200 similar or equal to 0.035 and is missing similar to 77% of the cosmologically available baryons. Consequently, Cen A should have a hot intergalactic medium with a mass of similar to 8 x 10(11) M-circle dot, which is more than similar to 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.