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A key issue in astronomy is to understand galaxy formation and evolution, including the formation and evolution of the stellar population of the galaxies. Another key issue is distance determination. The Fundamental Plane (Djorgovski & Davis 1987, Dressler et al. 1987b) for E and S0 galaxies provides valuable insight into both problems. The Fundamental Plane (FP) is the relation ${\log{r_{\rm e}}}= \alpha \log\sigma + \beta \log{< \hspace{-3pt} I \hspace{-3pt}>_{\rm e}}+ \gamma$, where ${r_{\rm e}}$ is the effective (i.e. half-light) radius, ${< \hspace{-3pt} I \hspace{-3pt}>_{\rm e}}$ is the mean surface brightness within ${r_{\rm e}}$, and $\sigma$ is the central velocity dispersion.

The existence of the FP, the low scatter in it, as well as its slope are properties that a successful theory of galaxy formation and evolution should be able to explain. (Different theories for the interpretation of the FP are briefly reviewed in Sect. [*].) This also goes for other relations between global parameters for E and S0 galaxies, such as the ${ {\rm Mg}_2}$-$\sigma$ relation.

The ${D_{\rm n}}$-$\sigma$ relation (which is closely related to the FP, as explained in Sect. [*]) has been used to determine distances and deviations from the pure Hubble expansion of the Universe for a large number of galaxies by the `7 Samurai' group (Dressler et al. 1987a, Lynden-Bell et al. 1988, Faber et al. 1989). These authors found systematic deviations from the pure Hubble expansion, with the galaxies streaming towards the Hydra-Centaurus region. This streaming motion was interpreted as originating from a huge mass concentration ( $\sim 5 \times 10^{16} M_\odot$, Lynden-Bell et al. 1988) coined the `Great Attractor' (see also Faber & Burstein 1988).

However, the reality of the Great Attractor was not agreed upon. This dispute was one of the main reasons for Jørgensen and collaborators to undertake their observing program to study E and S0 galaxies. The group has presented surface photometry in Jørgensen, Franx, & Kjærgaard (1992, hereafter JFK92), Jørgensen and Franx (1994, hereafter JF94), and Jørgensen, Franx, & Kjærgaard (1995a, hereafter JFK95a). Spectroscopy has been presented in Jørgensen, Franx, & Kjærgaard (1995b, hereafter JFK95b) and Jørgensen (1997a, hereafter J97). Analysis of the data has been presented in Jørgensen, Franx, & Kjærgaard (1993, hereafter JFK93), JF94, Jørgensen, Franx, & Kjærgaard (1996, hereafter JFK96), and J97.

A new direction in the work started by Jørgensen and collaborators is to study the properties of E and S0 galaxies using large and complete magnitude limited samples. Only for complete samples it is possible to draw reliable conclusions about the physical properties of the galaxies, regarding e.g. the distribution of metallicities, abundance ratios, ages, and relative disk luminosities. With the new spectroscopy on galaxies in Coma to be published in Jørgensen (1997b, in prep.), a large and highly complete magnitude limited sample is available. This Coma sample is used in the analysis presented in this work. Likewise, the HydraI data presented in this work are part of magnitude limited sample of high completeness.

It should be noted that I did the basic reductions, most of the surface photometry, and the derivation of the global photometric parameters for the HydraI data. Inger Jørgensen did the HydraI spectroscopy reductions. The Coma data were taken from the literature and from work not yet published (Jørgensen 1997b, in prep.).

next up previous contents
Next: Document Overview Up: 1. Introduction Previous: Preface

Properties of E and S0 Galaxies in the Clusters HydraI and Coma
Master's Thesis, University of Copenhagen, July 1997

Bo Milvang-Jensen (