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Title: Tracing S0 galaxies' evolution using planetary nebulae kinematics
Author: Cortesi, Arianna
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2011
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The stellar kinematics of the spheroids and disks of SO galaxies contain clues to their formation histories. Unfortunately, it is difficult to study these components using con- ventional absorption line spectroscopy - it is difficult to disentangle the two compo- nents and to recover the stellar kinematics in the faint outer parts of the galaxies. This thesis presents data on the stellar kinematics of 6 SO galaxies, in a range of environ- ments, derived from observations using the Planetary Nebula Spectrograph. These datasets allow the study of the kinematics of the faint outer parts of the galaxies, using planetary nebulae as tracers of the stellar populations. We have developed a new maximum-likelihood method that combines these data with a photometric spheroid-disk decomposition, in order to separate the kinematics of the two components. The method was tested on a simulated galaxy to ensure it correctly recovered the galaxy kinematics in the disk and the spheroid. This method is applied to NGC 1023 and the results are compared to a previous kine- matic analysis in the literature. We show that the unusual kinematics previously in- ferred for this galaxy were the result of not separating the disk and spheroid compo- nents. NGC 1023 is in fact found to exhibit spiral-like kinematics, once its components are properly decomposed. The maximum-likelihood clipping applied in the method also reveals a star stream associated with NGC 1023A, confirming the method's ro- bustness against such contaminants and its ability to uncover additional kinematic components. The method is then applied to the full sample of 6 SOs and we show that, with one exception, they have flat rotation curves, ordered motions dominate ran- dom motions in the disks, and the spheroid velocity dispersions remain approximately constant with radius. The derived kinematic parameters are studied and compared to those of spiral and el- liptical galaxies. The inferred circular speeds, after applying the asymmetric drift cor- rection, are in good agreement with those derived directly from gas kinematics, where such data are available. Although primarily rotationally supported, the disks are found to have systematically larger random motions than typical spiral galaxies, with this dif- ference most apparent in the SOs with the largest bulges. By investigating the Tully- Fisher and Faber-Jackson relations for the decomposed disks and spheroids respec- tively, we find that these SOs have systematically fainter disks and brighter spheroids than spiral galaxies and ellipticals in the literature. All these results are consistent with a scenario in which SO galaxies are formed from spirals through a moderately-violent mechanism, such as a series of very minor mergers.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available