The Formation and Evolution of S0 Galaxies

Abstract

This thesis studies the origin of local S0 galaxies and their possible links to other morphological types. To address these issues, two different approaches have been adopted: a detailed study of the stellar populations of S0s in the Fornax Cluster and a study of the Tully-Fisher Relation (TFR) of local S0s in different environments. The analysis of the central absorption line indices of 9 S0 galaxies in the Fornax Cluster indicates that they correlate with central velocity dispersions (sigma0). However, the stellar population properties of these S0s indicates that the observed trends seem to be produced by relative differences in age and alpha-element abundances and not in metallicity as previous studies have found in ellipticals. The observed scatter in the line indices versus sigma0 relations can be partially explained by the rotationally-supported nature of many of these systems. It was also confirmed that the dynamical mass is the driving physical property of all these correlations and in our Fornax S0s it has to be estimated assuming rotational support. A study of the local B- and Ks-band TFR in S0 galaxies shows that these objects lie systematically below the TFR for nearby spirals in both the optical and infrared bands. This offset can be crudely interpreted as arising from the luminosity evolution of spiral galaxies that have faded since ceasing star formation. However, a large scatter is also found in the S0 TFR, which means that these galaxies cannot have formed exclusively by this simple fading mechanism after all transforming at a single epoch. For the Fornax Cluster data, the offset from the TFR correlates with the estimated age of the stars in the centre of individual galaxies implying that part of the scatter in the S0 TFR arises from the different times at which galaxies began their transformation