The fundamental line of the local group satellites

We present a new correlation between the mass-to-light (M/L) ratio and the mean metallicity for the satellites of the Local Group. This relation, together with their central surface brightness, defines a fundamental line where metal-poor and low surface brightness dwarf galaxies are dark matter dominated while metal-rich high surface brightness systems will have a low M/L ratio. This fundamental line is independent of distance to the central galaxy (M31 and the Milky Way) and morphological type, among other global parameters, as their star formation history. The new M/L-metallicity relation indicates that dwarf spheroidal galaxies are dark matter confined and L that their high M/L ratios are not a result of the tidal loss of stars. It can be interpreted that these satellites L experienced a continuous loss of metals with a final episode of gas ejection at the end of the star formation epoch. Only globular clusters are found to lie outside the fundamental line of dwarf satellites. Unlike satellite galaxies, they are not dark matter confined.