Core sub-structure of elliptical galaxies : the core resolution technique applied to NGC 1399.

Abstract

UBRJK' images, obtained with subarcsecond seeing, are presented and used to derive the core light profile of the elliptical galaxy NGC 1399. These data, combined with an HST PC V band exposure, and high- resolution velocity dispersion data obtained by us are used to show that NGC 1399 is likely to possess a central dark mass concentration. Models with a constant mass-to-light ratio cannot fit the available data and be stable with respect to the radial orbit instability. The core resolution technique applied to the ground based data reveals a central intensity spike, consistent with our predictions (Moller et al. 1993a,b). The data are fully compatible with a colour independent spikyness, U through K', even though weak evidence is found for a possible increase in spikyness towards the UV. Detailed model fitting to both the ground based and HST data gives results identical to those obtained from the the core resolution technique, hence verifying its applicability, and potential value.