The Nuclear Cusp Slopes of Dwarf Elliptical Galaxies

Abstract

We derive the light profiles for a sample of 25 dwarf elliptical galaxies observed by us with Hubble Space Telescope's Wide Field and Planetary Camera 2 in F555W and F814W. These profiles are fitted with Nuker, R^1/4, exponential, and Sersic laws and are also used to derive the nuclear cusp slopes γ. We discuss the correlation of nuclear cusp slope with galactic luminosity, the presence of a nucleus, and the type of light profile. The results are compared with those found in the literature for elliptical galaxies and the bulges of spiral galaxies. We find that, as a class, the nuclear regions of dwarf ellipticals are very similar to those of the exponential bulges of spiral galaxies and have nuclear cusp slopes shallower than those of bulges with the same luminosity that were well fitted by a de Vaucouleurs R^1/4 profile. For the 14 nucleated galaxies in our sample, this conclusion is less certain than for the 11 nonnucleated objects, since it relies on an extrapolation of galaxy light under the nucleus. In terms of their light profiles and nuclear properties, most spheroidal stellar systems can be broadly divided into two subclasses: the exponential shallow cusp objects and the R^1/4 steep cusp objects. Membership of a class does not appear to correlate with the presence of a massive stellar disk. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.