The Magellanic Clouds: their evolution,structure and composition

Summary The Magellanic Clouds play a fundamental role in a number of fields of astronomical research. Their distances are most relevant to the extragalactic distance scale. Their relative proximity offers exceptional opportunities for detailed studies of their stellar and interstellar content. They serve therefore as testing grounds for modern astrophysical theories, in particular concerning the chemical evolution of stars and galaxies.In this review we will discuss recent attempts to determine accurate distances to the Magellanic Clouds. We will consider their stellar generations as the results of interactions between the Large and the Small Magellanic Cloud as well as between the Clouds and the Galaxy. Recent determinations of the chemical abundances of the various age groups will be presented. The fact that the evolution of the Clouds has been slower than that of our Galaxy gives us the opportunity to study the conditions in slightly metalpoor galaxies. Recent progress in observing techniques has added much to our knowledge about the interstellar medium of the Clouds.The Magellanic System, which comprises the Magellanic Clouds, the Inter-Cloud Region and the Magellanic Stream, will be described. We will in particular consider the complex structure of the Large and the Small Cloud and the kinematics of their populations.     

AGN feedback through sound wave dissipation

We investigate the possibility of explaining the observed ripples in the X-ray gas in the Perseus and Virgo clusters through natural oscillations of a perturbed radio cocoon. Such a perturbation would result from an expanding overpressured cocoon of radio plasma overshooting its pressure equilibrium point with the cluster gas. The oscillations are heavily acoustically damped, and energy injection rates required to sustain them are consistent with observed AGN powers. Viscous dissipation of sound waves generated by these oscillations heats the cluster gas. By comparing our model with observations in Perseus and Virgo, we reproduce the observed ripple separations and amplitudes. Spitzer viscosity is largely sufficient in explaining the gas density profile, suggesting that thermal conductivity is likely to be heavily suppressed. In the central regions, viscous heating can suppress cooling flows on timescales exceeding the radio source lifetime.