10 Concluding remarks

We have summarized the properties of the different components of the central galaxy NGC 1399 (GCS, cD halo, bulge) and the dwarf galaxy population in the center of the cluster. We have analysed under which circumstances the GCS and cD halo can be explained by the infall and accretion of gas-poor as well as gas-rich dwarf galaxies.

Estimations of the GC formation efficiency from infalling gas, and simulations of the accretion of GCSs from early-type dwarfs have shown that the building-up of the cD halo and central GCS by dwarf galaxy and gas infall alone is only possible under special conditions during the formation and evolution of the cluster. Depending on the leading process which contributed most to the rich GCS, the following conditions are required to fulfil the observed properties:

• There are as many blue (metal-poor) as red (metal-rich) GCs seen around NGC 1399. Since not all metal-rich GCs can be assigned to the bulge of NGC 1399 when adopting a reasonable S_N, the formation of secondary metal-rich GCs from stripped gas (or within the dwarf galaxies) probably was an effective process besides the capture of metal-poor GCs.
• The stripping and capture of GCS of gas-poor dwarf galaxies can only account for the metal-poor GC population.
• If the accretion of gas-poor dwarfs was a dominating process, the faint end slope of their initial LF had to be as steep ($\alpha < -1.4$) as it is predicted in CDM models in order to provide a sufficient number of dwarfs that have been disrupted in the central galaxy.
• A steep faint end slope of the initial LF leads to a mean metallicity of the captured dwarfs that is about 0.5 dex more metal-poor than the observed value of the blue GC population around NGC 1399.
• Furthermore, in the accretion dominated scenario, an unlikely high number of dwarfs ($\simeq 6000$, see Table 5) had to be accreted, and about 50% of the fainter dwarfs (-12.5 < M_V < -10.5) must have possessed at least one GC in order to produce high S_N values.
• A very efficient increase in S_N of the central GCS by the formation of GCs from gas can be achieved, if the cluster formation efficiency was as high as in merging or starburst galaxies.
• If the majority of the GCs (metal-poor as well as metal-rich ones) formed from stripped gas, a significant fraction of the gas was enriched to at least -1.0 dex before forming GCs in order to explain the bimodal metallicity distribution of the central GCS. This implies that the metal-rich GCs should be at least 2 Gyr older than the metal-poor ones and should show a significant age spread.

Certainly, some of the requirements are quite restrictive. We conclude that the infall of dwarf galaxies can principally explain many properties in the center of the Fornax cluster, but is most probably not the only process that has been active. Certainly, also the brighter, more massive galaxies were envolved by the interaction processes in the central region of the Fornax cluster. A natural extension of the dwarf galaxy infall scenario is, for example, the stripping (and early merging) of giant galaxies - ellipticals and spirals (as mentioned in Sect. 8.2). Besides the low-luminosity ellipticals in Fornax, very likely candidates for stripping are the central giant galaxies NGC 1380 and NGC 1404, which have low GC specific frequencies, and might therefore have provided a significant fraction of the central GCS (see Kissler-Patig et al. 1999).

We are aware of the fact that our proposed scenario has to be tested and confirmed by further theoretical as well as observational work. Especially, it has to be shown in N-body simulations whether the accretion rate of dwarf galaxies can be very high, and what is the dynamical behaviour of stripped and accreted GCs in the central cluster potential. Furthermore, it has to be tested under which conditions a high cluster formation efficiency can be obtained from stripped gas (whether it is comparable to a starburst situation in a galaxy or not). On the observational side it has to be shown, whether the faintest dwarf galaxies possess GCs or not. Further investigation of the faint end slopes of galaxy LFs for clusters with very different properties (redshift, richness, compactness, existence of a cD galaxy, etc.) will show whether the proposed scenario is compatible with the findings. Observations more sensitive to the ages of GCs (i.e. measurement of line indices) will prove or disprove the predictions of an age spread among the GCs.

Acknowledgements

This research was partly supported by the DFG through the Graduiertenkolleg "The Magellanic System and other dwarf galaxies'' and through grant Ri 418/5-1 and Ri 418/5-2. MH thanks Fondecyt Chile for support through "Proyecto FONDECYT 3980032'' and LI for support through "Proyecto FONDECYT 8970009''.