Many dwarf galaxies are observed to be nucleated. But some dwarf galaxies, primarily those that are located beyond the core radius of clusters of galaxies, do not appear to be nucleated. We revisit the scenario that the formation of dwarf galaxiesÏ nuclei is due to the orbital decay of globular clusters within them and suggest that the observed dichotomy and spatial dependence of dwarf galaxy morphology is due to the nature and the relative strength of the extragalactic tidal perturbation.

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... gh a series of numerical simulations, we show that in dwarf galaxies with a relatively weak external tidal perturbation dynamical friction can lead to signiÐcant orbital decays of globular clusters and the formation of compact nuclei within a Hubble timescale. Similar tendencies also occur in those dwarf galaxies near the center of clusters of galaxies where the extragalactic tidal perturbation tends to preserve the integrity of dwarf galaxies. Based on these numerical simulations, we show that the observed central structures of four nucleated dwarf galaxies in the Virgo Cluster are well modeled by superimposing a small number of globular clusters onto the background stellar distribution. We also deduce a Ñat mass-weighted velocitydispersion distribution that is consistent with some recent observations and suggest that the cores of nucleated dwarfs may be slightly o † center within D1 Gyr after each globular cluster merger event. In the outskirts of clusters of galaxies external tidal perturbation tends to disrupt dwarf galaxies and prevent the sedimentation of the globular clusters within them. We speculate that the residual nucleated dwarf galaxies near the central regions of the Virgo Cluster of galaxies may be the Ðrst entities to have congregated and remained there. Such a scenario is consistent with the cold dark matter hypothesis for galaxy formation.