Cores and power-law profiles

Lauer et al. (1995) have used the Planetary Camera of the HST to image the central regions of 57 early-type galaxies. They found that the radial surface brightness profiles of most of these fall into two distinct classes: (1) galaxies that have cores, and (2) galaxies that exhibit power-law profiles that continue down to radii near the resolution limit. Of the galaxies observed by Lauer et al. 15 have cores and 30 exhibit power-law profiles. Among the galaxies that have been classified as having either cores or power-law profiles 21 are contained in A Revised Shapley–Ames Catalog of Bright Galaxies (Sandage & Tammann 1981). Since the statistics of objects in this catalog are better understood than those of the entire sample, only the nine galaxies with cores and the 12 having power-law profiles that are in the Shapley–Ames Catalog will be considered below. The most striking feature of these data (which has already been commented on by Lauer et al. and others) is that the galaxies with cores tend to be more luminous than those with power-law profiles. For the Shapley–Ames sub-sample a Kolmogorov–Smirnov test rejects the hypothesis that the galaxies with bulges were drawn from the same luminosity distribution as those having power-law profiles at the 97% confidence level.