The nearby elliptical galaxy Cen A is surrounded by a flattened system ofdwarf satellite galaxies with coherent motions. Using a novel Bayesianapproach, we measure the mean rotation velocity $v_{\rm rot}$ and velocitydispersion $\sigma_{\rm int}$ of the satellite system. We find $v_{\rmrot}/\sigma_{\rm int} \simeq 0.7$ indicating that the satellite system hasnon-negligible rotational support. Using Jeans' equations, we measure acircular velocity of 258 km s$^{-1}$ and a dynamical mass of $1.2\times10^{13}$ M$_\odot$ within 800 kpc. In a $\Lambda$CDM cosmological context, wefind 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 largerthan current X-ray estimates. Intriguingly, The whole Cen A group lies on thebaryonic Tully-Fisher relation defined by individual rotationally supportedgalaxies, as expected in Milgromian dynamics (MOND) with no need of missingbaryons.

The combination of gas-phase oxygen abundances and stellar metallicities canprovide us with unique insights into the metal enrichment histories ofgalaxies. In this work, we compare the stellar and gas-phase metallicitiesmeasured within a 1$R_{e}$ aperture for a representative sample of 472star-forming galaxies extracted from the SAMI Galaxy Survey. We confirm thatthe stellar and interstellar medium (ISM) metallicities are stronglycorrelated, with scatter $\sim$3 times smaller than that found in previousworks, and that integrated stellar populations are generally more metal-poorthan the ISM, especially in low-mass galaxies. The ratio between the twometallicities strongly correlates with several integrated galaxy propertiesincluding stellar mass, specific star formation rate, and a gravitationalpotential proxy. However, we show that these trends are primarily a consequenceof: (a) the different star formation and metal enrichment histories of thegalaxies, and (b) the fact that while stellar metallicities trace primarilyiron enrichment, gas-phase metallicity indicators are calibrated to theenrichment of oxygen in the ISM. Indeed, once both metallicities are convertedto the same `element base' all of our trends become significantly weaker.Interestingly, the ratio of gas to stellar metallicity is always below thevalue expected for a simple closed-box model, which requires that outflows andinflows play an important role in the enrichment history across our entirestellar mass range. This work highlights the complex interplay between stellarand gas-phase metallicities and shows how care must be taken in comparing themto constrain models of galaxy formation and evolution.