Galaxy scaling relations from the ACS Virgo and Fornax Cluster Surveys: no evidence for a dwarf-giant dichotomy

Abstract We examine the photometric and structural properties of early-type galaxies derived from theACS Virgo and Fornax Cluster Surveys, supplementing these data with previously published or newly reanalysed data for additional early-type galaxies in Virgo, Fornax and the Local Group. As we have noted elsewhere, Sérsic models are found to provide accurate representations of the observed brightness profiles on scales greater than a few percent of the effective radius,Re. On smaller scales, the brightness profiles of bright (MB≳ −20) galaxies show centraldeficitswith respect to the inward extrapolation of the Sérsic models; fainter galaxies usually show centralexcesses. Fainter thanMB≈ −20, we find a continuity in the photometric and structural scaling relations: i.e., between absolute magnitude, central surface brightness, Sérsic index, effective radius, and the surface brightness measured at, and averaged within, the effective radius. There is no evidence for a “dwarf/giant dichotomy” — a conclusion consistent with a number of recent studies but contrary to some earlier claims.