Recovering lenticular galaxies past histories using planetary nebulae kinematics: the case of NGC1023
We present a detailed study of the lenticular galaxy NGC 1023 kinematics. To perform this analysis we use planetary nebulae (PNe). which can be observed in the faint outer regions of the galaxy, where traces of the galaxy past history are clearly recorded. If the circular speed is equal or lower than the stars velocity dispersion, the system is hot and it is the result of a minor merger. Otherwise, if the stellar motions are rotation dominated at large radii, a spiral galaxy is the progenitor of the lenticular. A first attempt at such an analysis was undertaken by Noordermeer et al. (2008), who found that the S0 system NGC 1023 has very peculiar kinematics in its disk, which do not seem to be consistent with either of the above scenarios. In this paper we show that that result was largely due to a contamination of the disk kinematics by stars belonging to the spheroidal component or accreted from the small companion. We present a new method based on a more sophisticated maximum-likelihood analysis that uses a full two-dimensional disk/spheroid decomposition to solve simultaneously for both disk and spheroid kinematics. This analysis reveal that NGC1023 has the kinematics expected for a stripped spiral galaxy.
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University of Nottingham, UK