Early-type dwarf galaxies in the virgo cluster : nature or nurture?

Abstract

In order to provide a concise overview of our main conclusions without just repeating the individual summary of each chapter, we decided to highlight again those figures that we believe to contain the most important results of our research. Figure 2.8: What creates and determines the shape of the spiral arms that are seen in some dEs? Our derived pitch angles, as well as the grand-design structure of the arms, clearly show that they cannot just be the remainder of the spiral arms of potential late-type progenitor galaxies. Figure 3.9: While a young stellar population dominates the light at the centers of the dE(bc)s, 90% or more of the mass is made up by an old stellar population. Not long after cessation of star formation, these galaxies will just be ordinary dEs. Figure 4.2: Several dE subclasses exist that have different shapes and different distributions within the cluster, defining a morphology-density relation within the dE class. Figure 5.18: The colour-magnitude relation of the Virgo cluster dEs depends slightly, yet significantly, on local environmental density. Figure 5.29: While the shape and distribution of the dE(di)s are much more like those of the bright dE(nN)s than like those of the dE(N)s, their stellar populations are similar to those of the dE(N)s, which in turn are significantly different from those of the dE(nN)s. Figure 6.27: A region of higher stellar population ages of the dE(N)s is located south-east from the cluster center. It is consistently seen both for the low and the high-density subsample, and coincides with a region of stronger X-ray emission. Figure 7.5: Complementing optical with near-infrared photometry enables a much more reliable analysis of ages and metallicities, and reveals a rather narrow sequence of dEs in colour space. Even though we speculated in the previous chapter about possible evolutionary links between certain subclasses, the bottom line of our study is that the dEs are not a homogeneous class of galaxies, and can not be explained with just a single formation mechanism.