Near-infrared images of a sample of red, blue and giant low surface brightness disk galaxies (LSBGs) were combined with optical data with the aim of constraining their star formation histories. Most LSBGs have strong colour gradients consistent with mean stellar age gradients. We find that LSBGs have a large range of ages and metallicities, spanning those observed in normal disk galaxies. In particular, red and blue LSBGs have very different star formation histories and represent two independent routes to low B band surface brightness. Blue LSBGs are well described by models with low, roughly constant star formation rates, whereas red LSBGs are better described by a ‘faded disk’ scenario.

This poster paper presents an extension of the entropy-driven model of cluster evolution developed by Bower, 1997 (MN, 288, 355) in order to study the evolution of clusters in a low density universe. Our approach allows us to explicitly seperate the contributions from gravitational collapse and changes in the core entropy of the intracluster gas. Here, we apply the model to determine whether a preferred value of Ω0 is selected by currently available constraints (Figure 1). Measurements of the X-ray evolution of clusters cannot, by themselves, select out a particular cosmological model. An additional constraint on the effective power spectrum index (n) is required. This can either come from a measurement of the large-scale galaxy correlation function or from the shape of the present-day temperature function. A theoretical calculation of the Ω0 dependence of the power spectrum does not help break the inherent degeneracy.