The effect of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies

We study the effects of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies, in particular focusing on two model galaxies similar to IZw18 and NGC 1569. We consider both scenarios, clouds put at the beginning of the simulation and continuously created infalling ones. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr, but during this time they act as an additional cooling agent and the internal energy of cloudy models is typically reduced by 20-40 % in comparison with models without clouds. The clouds delay the development of large-scale outflows, therefore helping to retain a larger amount of gas inside the galaxy. However, especially in models with continuous creation of infalling clouds, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity (by up to similar to 0.4 dex) with respect to the one attained by diffuse models. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim