THE CENTERS OF EARLY-TYPE GALAXIES WITH HST .3. NONPARAMETRIC RECOVERY OF STELLAR LUMINOSITY DISTRIBUTIONS

We have non-parametrically determined the luminosity density profiles and their logarithmic slopes for 42 early-type galaxies observed with HST. Assuming that the isodensity contours are spheroidal, then the lu minosity density is uniquely determined from the surface brightness da ta through the Abel equation. For nearly all the galaxies in our sampl e, the logarithmic slope of the luminosity density (S=d log v/d log r) measured at 0.1'' (the innermost reliable measurement with the uncorr ected HST) is significantly different from zero; i.e., most elliptical galaxies have cusps. There are only two galaxies for which an analyti c core (S --> 0) cannot be excluded. The distribution of logarithmic s lopes at 0.1'' appears to be bimodal, confirming the conclusion of Lau er et al. [AJ, 110, 2622 (1995)] that early-type galaxies can be divid ed into two types based on their surface brightness profiles; i.e., th ose with cuspy cores and those whose steep power-law profiles continue essentially unchanged in to the resolution limit. The peaks in the sl ope distribution occur at S = -0.8 and -1.9, More than half of the gal axies have slopes steeper than -1.0. Taken together with the recent th eoretical work of Merritt and Fridman, these results suggest that many (and maybe most) elliptical galaxies are either nearly axisymmetric o r spherical near the center, or slowly evolve due to the influence of stochastic orbits. (C) 1996 American Astronomical Society.