The Cen A galaxy group: dynamical mass and missing baryons
  The nearby elliptical galaxy Cen A is surrounded by a flattened system of
dwarf satellite galaxies with coherent motions. Using a novel Bayesian
approach, we measure the mean rotation velocity $v_{\rm rot}$ and velocity
dispersion $\sigma_{\rm int}$ of the satellite system. We find $v_{\rm
rot}/\sigma_{\rm int} \simeq 0.7$ indicating that the satellite system has
non-negligible rotational support. Using Jeans' equations, we measure a
circular velocity of 258 km s$^{-1}$ and a dynamical mass of $1.2\times
10^{13}$ M$_\odot$ within 800 kpc. In a $\Lambda$CDM cosmological context, we
find that the Cen A group has a baryon fraction $M_{\rm b}/M_{200}\simeq0.035$
and is missing $\sim$77$\%$ of the cosmologically available baryons.
Consequently, Cen A should have a hot intergalactic medium with a mass of
$\sim$8$\times$10$^{11}$ M$_\odot$, which is more than $\sim$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.
