The Astronomical Journal, 127:1917-1942, 2004. Paper Website abstract bibtex
We fitted the surface-brightness profiles of 21 elliptical galaxies using both the Sersic function and a new empirical model that combines an inner power law with an outer S√©rsic function. The profiles are combinations of deconvolved Hubble Space Telescope (HST) profiles from the literature and ellipse fits to the full WFPC2 mosaic images and thus span a radial range from ~0.02" to about twice the half-light radius. We are able to accurately fit the entire profiles using either the S√©rsic function or our new model. In doing so, we demonstrate that most, if not all, so-called ``power-law'' galaxies are better described as ``S√©rsic galaxies''-they are well modeled by the three-parameter S√©rsic profile into the limits of HST resolution-and that ``core'' galaxies are best understood as consisting of an outer S√©rsic profile with an inner power-law cusp, which is a downward deviation from the inward extrapolation of the S√©rsic profile. This definition of cores resolves ambiguities that result when the popular ``Nuker law'' is fitted to the profiles of ellipticals and bulges, particularly at lower luminosities. We also find that using the Nuker law to model core-galaxy nuclear profiles systematically overestimates the core radii by factors of 1.5-4.5 and underestimates the inner power-law slope by ~20%-40% or more.