The ACS Virgo Cluster Survey. VI. Isophotal Analysis and the Structure of Early‐Type Galaxies

Abstract

We present a detailed analysis of the morphology, isophotal parameters, and surface brightness profiles for 100 early-type members of the Virgo Cluster, from dwarfs ( M B = -15.1 mag) to giants ( M B = -21.8 mag), imaged in the g and z passbands using the Advanced Camera for Surveys on board the Hubble Space Telescope . Dust and complex morphological structures are common. Dust is detected in 42% of galaxies brighter than B T = 12.15 mag, while kiloparsec-scale stellar disk, bars, and nuclear stellar disks are seen in 60% of galaxies with intermediate luminosity. Isophotal parameters are derived typically within 8 kpc from the center for the brightest galaxies, and 1.5 kpc for the faintest systems, with a resolution of 7 pc. For most galaxies, the surface brightness profiles are well described by a Sérsic model with index n that increases steadily with the galaxy luminosity; only for 8 of the 10 brightest galaxies are the inner profiles (typically within 100 pc of the center) lower than expected based on an extrapolation of the outer Sérsic model, and are better described by a single power-law function. Contrary to previous claims, we find no evidence in support of a strong bimodal behavior of the logarithmic slope of the inner surface brightness profile, γ; in particular the γ distribution for galaxies that do not show evidence of multiple morphological components is unimodal across the entire magnitude range spanned by the ACSVCS galaxies. Although the brightest galaxies have shallow inner profiles, the shallowest profiles are found in faint dwarf systems. The widely adopted separation of early-type galaxies between "core" and "power-law" types is questioned based on the present study.