Observational test of environmental effects on the local group dwarf spheroidal galaxies

In this Letter, we examine whether tidal forces exerted by the Galaxy or M3 1 have an influence on the Local Group dwarf spheroidal galaxies (dSph's) t hat are their companions. We focus on the surface brightness profiles of th e dSph's, especially their core radii, because it is suggested, based on th e numerical simulations, that tidal disturbance can make core radii extende d. We examine the correlation for the dSph's between the distances from the ir parent galaxy (the Galaxy or M31) and the compactnesses of their surface brightness profiles by using a parameter C defined newly in this Letter. C onsequently, we find no significant correlation. We make some remarks on th e origin of this result by considering three possible scenarios-the tidal p icture, the dark matter picture, and the heterogeneity of the group of dSph s-each of which has been often discussed as a way of understanding the fund amental properties and formation processes of dSphs.