Detecting Stellar Streams in the Halos of Galaxies with Voronoi Tessellations

Galaxy formation models oriented towards a ACDM cosmology envision galaxies as being built through the accretion of dwarf galaxies. Such galaxy accretion should appear as tidally-disrupted streams of stars in the halo of the host galaxy. Yet these stellar streams have very low surface brightnesses, making their detection difficult. We propose that surface luminosity maps, derived from Hubble space telescope advanced camera for surveys resolved star photometry, can be used to reveal stellar structures in the halos of galaxies. To create surface luminosity maps with high, yet consistent, signal to noise, the centroidal Voronoi tessellation is used. The Voronoi tessellation offers the advantage of optimal binning to preserve spatial resolution. As preliminary testing has shown, the technique reveals halo structures, such as the dwarf galaxy near NGC 4631, as bright, compact, Voronoi regions.