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C.M. Carollo (Columbia University), M. Franx (Leiden Observatory), G.D. Illingworth (UCSC)
\noindent Around 20% of ellipticals have kinematically distinct cores (KDCs): in these galaxies, the rotation measured close to the nucleus is markedly different from the outer one. The properties can be rather extreme: in the prototypical KDC, IC 1459, the stars in the core region rotate counter to those in the outer parts, and the central rotation curve measured from the ground reaches 180 km/s.
We have obtained {\tt STIS} spectra of IC 1459, NGC 1700, and NGC 4365, 3 KDCs out of a sample of 15 that we had previously studied by means of multicolor {\tt WFPC2} images. The 3 STIS targets were selected so as to represent different nuclear behaviours in the KDC population: NGC 1700 shows a steep nuclear stellar cusp; its isophotes are slightly boxy at the scale of the counter-rotating component, and disky at larger radii. NGC 4365 has a shallow stellar cusp and hosts in its center a resolved ~ 15pc-region which is bluer than the surrounding regions. IC1459 shows an intermediate nuclear cuspiness and hosts a blue unresolved spike, likely of non-thermal origin.
We are using our {\tt STIS} data to probe the kinematics of the distinct cores down to the smallest scales (10 pc). The STIS spectroscopic data will allow us to answer the following questions: (i) What are the rotational amplitudes of the counter-rotating components close to the nucleus? (ii) Are the length scales of these components related to the ``break radius'', i.e., the photometric length scale of the nuclear cusp? (iii) Do these galaxies host central black holes (BHs), and how do their BH masses compare to those of BHs hosted by normal galaxies of the same luminosity? (iv) Is there any indication for ``strange'' stellar populations, these being either young, or metal poor, or extremely metal rich? The answers to these questions will provide crucial insight into the general problem of core/cusp formation, as the formation of these nuclei must have been very extreme.