The central regions of galaxy clusters are the places with the highest galaxy density in the universe. Dwarf ellipticals (dE) are especially the most strongly clustered types of galaxies in high-density environments (e.g. review by Ferguson & Binggeli 1994, and references therein). Several striking characteristics are seen in the center region of clusters: (1) most central galaxies possess extraordinarily rich globular cluster systems (GCS) (see Harris 1991; Richtler 1995 and references therein), but see also apparent counter-examples (see Table 14 in McLaughlin et al. 1994); (2) there often exists a cD galaxy in the center of clusters (e.g. Schombert 1988). (3) different types of dwarf galaxies have different clustering properties (e.g. Vader & Sandage 1991); (4) in some cases the faint end slope of the dwarf galaxy luminosity function (LF) seems to depend on the cluster-centric distance (e.g. in Coma: Lobo et al. 1997). The question arises on whether these properties may be related through the accretion of dwarf galaxies.
The answer to this question is most probably associated to the formation epoch of galaxy clusters. At that time, it is expected that galaxies were very gas-rich and that interactions between galaxies were more frequent. The number density of galaxies at that epoch in the central region must have been larger than today. Therefore, the initial population of dwarf galaxies played an important role. The favoured theoretical models of galaxy cluster formation predict a steep slope of the initial mass function towards the low-mass end (see a more detailed discussion and references in Sect. 2.1). In contrast, the faint end slope of the observed LF in nearby groups and clusters is significantly flatter (see Ferguson & Binggeli 1994; Trentham 1998). One possibility that would explain this discrepancy is the accretion and dissolution of dwarf galaxies in cluster centers. It is possible to understand the formation of a rich GC system and a cD halo from the infall of gas-poor and gas-rich dwarfs into a dense cluster environment. During the infall of gas-poor as well as gas-rich dwarfs in a dense cluster center environment several scenarios are thinkable for forming a rich GCS and a cD halo (see Sect. 5).
Support for such a scenario from the observational side comes from López-Cruz et al. (1997) who compared the properties of clusters with and without a central luminous cD galaxy. They found that clusters without a prominent cD galaxy tend to have a steep LF at the faint end and a high fraction of late-type galaxies, and thus seem to be less evolved than clusters with pronounced cD galaxies and relatively flat LF at the faint end. They explain this finding by the disruption of dwarf galaxies.
In this study the attention is focused on the properties of the relatively poor, compact, and evolved Fornax cluster, one of the best studied galaxy clusters in the local universe (e.g. Ferguson 1989; Ferguson & Sandage 1988). Other nearby clusters are believed to be in different evolutionary states. Whereas Virgo (e.g. Sandage et al. 1985; Ferguson & Sandage 1991) is dominated by late type galaxies and is only half as dense in the center (numbers of galaxies per volume) as Fornax. Centaurus (Jerjen & Dressler 1997; Stein et al. 1997) and Coma (e.g. Secker & Harris 1997) show substructures, indicative of a still ongoing dynamical evolution, like for example cluster-cluster or cluster-group merging.
In the first two papers of this series (1998a, 1998b hereafter Paper I and Paper II) we investigated the distribution of galaxies in central Fornax fields. We found two compact objects that belong to the Fornax cluster and might be candidates for isolated nuclei of stripped dwarf ellipticals. However, very few new members were found compared to the study of Ferguson (1989). Thus, the spatial distribution and luminosity function of dwarf galaxies in Fornax (Ferguson & Sandage 1988) was confirmed.
In this paper we discuss the possibility, whether the infall of dwarf galaxy into the cluster center may play an important role in the enrichment of the central globular cluster system, especially the increase of the globular cluster specific frequency SN, as well as the formation of the extended cD halo.
In the following section we give a compilation of the necessary background of our analysis.
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