Although early observations with the Hubble Space Telescope (HST) pointed to a sharp dichotomy among earlytype galaxies in terms of the logarithmic slope γ′ of their central surface brightness profiles, several studies in the past few years have called this finding into question. In particular, recent imaging surveys of 143 early-type galaxies belonging to the Virgo and Fornax Clusters using the Advanced Camera for Surveys (ACS) on board HST have not found a dichotomy in γ′, but instead a systematic progression from central luminosity deficit to excess relative to the inward extrapolation of the best-fitting global Sérsic model. Given that earlier studies also found that the dichotomy persisted when analyzing the deprojected density profile slopes, we investigate the distribution of the three-dimensional luminosity density profiles of the ACS Virgo and Fornax Cluster Survey galaxies. Having fitted the surface brightness profiles with modified Sérsic models, we then deproject the galaxies using an Abel integral and measure the inner slopes γ3D of the resulting luminosity density profiles at various fractions of the effective radius Re. We find no evidence of a dichotomy, but rather, a continuous variation in the central luminosity profiles as a function of galaxy magnitude. We introduce a parameter, Δ3D, that measures the central deviation of the deprojected luminosity profiles from the global Sérsic fit, showing that this parameter varies smoothly and systematically along the luminosity function.
- Galaxies: clusters: individual (Virgo, Fornax)
- Galaxies: elliptical and lenticular, cD
- Galaxies: formation
- Galaxies: nuclei
- Galaxies: structure