Brought to Light: Disk and Clump Substructures in Dwarf Early-Type Galaxies

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging two data sets of dwarf ETGs that are members of the Virgo and Fornax galaxy clusters. These dwarf ETGs are characterized by having disk-like or clump-like substructure features that lie mostly hidden within the bright diffuse light of the galaxies. We present a newly developed method that aims to robustly identify and extract the substructure features embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components: the bright, dominant, diffuse component, and the much fainter, underlying substructure component. By applying it to the two dwarf ETG data sets, we quantify their substructure features, and find that they contribute only between 2% to 10% of the total galaxy light within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the substructures we introduce in mock galaxy images, even at low substructure-to-total light fractions of a few percent. To showcase potential applications of the method, we subject the extracted substructure components of the Virgo and Fornax data sets to a Fourier analysis and to a color analysis, respectively. Our results indicate that the Virgo cluster has a larger fraction of dwarf ETGs with disk substructures compared to the Fornax cluster, and that embedded spiral arm features are common in disky dwarf ETGs in Virgo but completely absent in Fornax. We propose that these differences are a reflection of the particular characteristics of each distinct cluster environment. We also find that disk substructures tend to be fainter and redder than clump substructures, possibly indicating that disky and clumpy dwarf ETGs may have had different origins and/or evolutionary histories. However, both sub-classes are consistent with being transition-type dwarf galaxies, where environmentally-driven processes are transforming them from late-types to early-types. Through this work, we conclude that the cluster environment must play a major role in shaping and transforming the dwarf galaxy populations in galaxy clusters