This is a random resampling of the data from the Gadget simulations of Debuhr et al. 2010. Red points are the initial stars making up the galaxy, yellow points are gas particles, and white points are newly formed stars. Not shown are the particles making up the dark matter halos.
A zip of a directory containing the snapshots of this simulation as text files (85 Mb zipped, 189 Mb unzipped) is contained here.